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Trigonometry, 2ADV T3 SM-Bank 7 MC

met2-2011-vcaa-15-mc 
 

The graph shown could have equation

  1. `y = 2cos(x + pi/6) + 1`
  2. `y = 2cos4(x - pi/6) + 1`
  3. `y = 4sin2(x - pi/12) - 1`
  4. `y = 3cos(2x + pi/6) - 1`
Show Answers Only

`=> B`

Show Worked Solution

`text{Amplitude = 2   (range from – 1 to 3)}`

`text{Graph centre line (median):}\ \ y= 1`

`:.\ text(Eliminate)\ \ C\ \ text(and)\ \ D.`
 

`text(Period) = (2pi)/3 – pi/6 = pi/2\ \ text{(from graph)}`

`text(Consider option)\ B,`

`text(Period)= (2pi)/n= (2pi)/4 = pi/2`

`=> B`

Filed Under: Trig Graphs (Y12) Tagged With: Band 4, smc-977-40-Unknown Trig Ratio

Trigonometry, 2ADV T3 SM-Bank 6 MC

The function with equation  `f(x) = 4 tan (x/3)`  has period

  1. `(2pi)/3`
  2. `6 pi`
  3. `3`
  4. `3 pi`
Show Answers Only

`D`

Show Worked Solution
`text(Period) ` `=pi/n`
  `= pi/(1/3)`
  `= 3 pi`

 
`=>   D`

Filed Under: Trig Graphs (Y12) Tagged With: Band 4, smc-977-30-tan

Trigonometry, 2ADV T3 SM-Bank 5 MC

The UV index, `y`, for a summer day in Newcastle East is illustrated in the graph below, where  `t`  is the number of hours after 6 am.
 

 
 

The graph is most likely to be the graph of

  1. `y = 5 + 5 cos ((pi t)/7)`
  2. `y = 5 - 5 cos ((pi t)/7)`
  3. `y = 5 + 5 cos ((pi t)/14)`
  4. `y = 5 - 5 cos ((pi t)/14)`
Show Answers Only

`B`

Show Worked Solution

`text{Centre line (median):}  \ y = 5`

`text(Amplitude) = 5`

`text(Period:)\ \ 14` `= (2 pi)/n`
`n` `= pi/7`

 

`:.\ text(Graph:)\ \ y = 5 – 5 cos ((pi t)/7)`

`=>   B`

Filed Under: Trig Applications (Y12) Tagged With: Band 4, smc-1188-30-Other Applications

Trigonometry, 2ADV T3 SM-Bank 4 MC

A section of the graph of  `f(x)`  is shown below.
 

VCAA 2012 6mc
 

The equation of  `f(x)`  could be

  1. `f (x) = tan (x)`
  2. `f (x) = tan (x - pi/4)`
  3. `f (x) = tan(2 (x - pi/4))`
  4. `f (x) = tan(2 (x - pi/2))`
Show Answers Only

`C`

Show Worked Solution

`text(Period) = pi/2`

`=>\ text(must be)\ C\ text(or)\ D`

`text(Shift)\ \ y = tan(x)\ \ text(right)\ \ pi/4.`

`=>   C`

Filed Under: Trig Graphs (Y12) Tagged With: Band 4, smc-977-30-tan

Measurement, STD2 M7 SM-Bank 12

Francis is buying a fridge. The energy usage of his two choices are below:

Fridge 1 (5 star rating): 227 kWh per year

Fridge 2 (2 star rating): 492 kWh per year

Each fridge has an expected life of 8 years.

If electricity costs 32.4 cents per kWh, how much will Francis save in electricity over the expected life of the more energy efficient fridge, to the nearest dollar?  (2 marks)

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Show Answers Only

`$687`

Show Worked Solution

`text(Energy cost of fridge 1)`

`= 227 xx 0.324 xx 8`

`= $588.38`

`text(Energy cost of fridge 2)`

`= 492 xx 0.324 xx 8`

`= $1275.26`

`:.\ text(Energy saving)` `= 1275.26 – 588.38`
  `= 686.88`
  `= $687`

Filed Under: Rates (Std2) Tagged With: Band 4, smc-805-20-Energy

Measurement, STD2 M7 SM-Bank 10

A potting mix is made up of two ingredients, potting soil and manure, in the ratio 5:2.

21 kilograms of potting mix are used to fertilise the  rectangular vegetable garden pictured below.
 


 

  1. What rate must the whole 21 kilograms of potting mix be applied to be spread evenly over the garden. Give your answer in grams per square metre.  (2 marks)

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  2. How much manure is needed to make the required potting mix?  (1 mark)

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Show Answers Only
  1. `150\ text(g/m²)`
  2. `text(6 kg)`
Show Worked Solution

i.   `text(Potting mix: 21 kg  ⇒  21, 000 grams)`

`text(Area of garden)` `= 20 xx 7`  
  `= 140\ text(m²)`  

 

`:.\ text(Rate)` `= (21\ 000)/140`
  `= 150\ text(g/m²)`


ii.
   `text(Ratio  5 : 2)\ \ =>\ \ 5/7 : 2/7`

`:.\ text(Amount of manure)` `= 2/7 xx 21`
  `= 6\ text(kg)`

Filed Under: Ratio and Scale (Std2) Tagged With: Band 4, smc-1187-10-Ratio (2 part)

Networks, STD2 N3 SM-Bank 42 MC

The network diagram below flows from the source (S) to sink (T).

Which of the edges is not at maximum capacity?
 


 

  1. `AC`
  2. `BC`
  3. `CT`
  4. `DT`
Show Answers Only

`=>\ text(C)`

Show Worked Solution

`text(Consider the minimum cut line: all edges are saturated.)`
 


 

`:.\ text(Edge)\ CT\ text(is not at maximum capacity.)`

`=>\ C`

Filed Under: Flow Networks and Minimum Cuts Tagged With: Band 4

Networks, STD2 N3 SM-Bank 46

A network diagram is drawn below.
 

 
 

  1. Calculate the maximum flow through this network.  (2 marks)

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  2. Copy the network above and illustrate the maximum flow capacity.  (2 marks)

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Show Answers Only
  1. `28`
  2.  
Show Worked Solution
i.   

 

`text(Maximum flow)` `=\ text(minimum cut)`
  `= 8 + 8 + 7 + 5`
  `= 28`

 

ii.   

Filed Under: Flow Networks and Minimum Cuts Tagged With: Band 4, smc-915-10-Min Cut/Max Flow, smc-915-30-Flow Capacity

Networks, STD2 N3 SM-Bank 39

Bianca is designing a project for producing an advertising brochure. It involves activities A-M.

The network below shows these activities and their completion time in hours.
 


 

  1.  What is the earliest starting time of activity J?  (1 mark)

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  2.  What is the latest starting time of activity H?  (1 mark)

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  3.  What is the float time of activity I?  (1 mark)

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  4.  What is the minimum time required to produce the brochure?  (2 marks)

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Show Answers Only
  1. `text(11 hours)`
  2. `text(18 hours)`
  3. `text(2 hours)`
  4. `text(34 hours)`
Show Worked Solution

i.   `text(Scanning forwards and backwards)`
 

 

`text{EST (activity}\ J) = 11\ text(hours)`

 

ii.    `text{LST (activity}\ H)` `=\ text{LST}\ (H)-text(weight)\ (H)`
    `= 20-2`
    `=18\ text(hours)`

 

iii.    `text{Float time}\ (I)` `=\ text(LST)\ (I)-text(EST)\ (I)`
    `=12-10`
    `= 2\ text(hours)`

 

iv.   `text(Critical Path is)\ CGJLM`

`:.\ text(Minimum time)` `= 2 + 9 + 6 + 7 + 10`
  `= 34\ text(hours)`

Filed Under: Critical Paths Tagged With: Band 4, Band 5, smc-916-30-Scanning Both Ways

Algebra, STD2 A4 SM-Bank 1 MC

The graph below represents  `y = a^x`.
 


 

What is the approximate value of  `2(a^5)`?

  1.   4
  2.   8
  3.  32
  4.  64
Show Answers Only

`B`

Show Worked Solution

`text(From graph:)`

`a^5` `=4`
`:. 2(a^5)` `= 2 xx 4`
  `= 8`

 
`=>\ text(B)`

Filed Under: Graphs and Applications (Y11), Non-Linear: Exponential/Quadratics (Std 2) Tagged With: Band 4, common-content, smc-830-10-Identify Graphs, smc-966-10-Exponential graphs

Calculus, SPEC2 2012 VCAA 5

At her favourite fun park, Katherine’s first activity is to slide down a 10 m long straight slide. She starts from rest at the top and accelerates at a constant rate, until she reaches the end of the slide with a velocity of `6\ text(ms)^(-1)`.

  1. How long, in seconds, does it take Katherine to travel down the slide?   (1 mark)

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When at the top of the slide, which is 6 m above the ground, Katherine throws a chocolate vertically upwards. The chocolate travels up and then descends past the top of the slide to land on the ground below. Assume that the chocolate is subject only to gravitational acceleration and that air resistance is negligible.

  1. If the initial speed of the chocolate is 10 m/s, how long, correct to the nearest tenth of a second, does it take the chocolate to reach the ground?   (2 marks)

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  2. Assume that it takes Katherine four seconds to run from the end of the slide to where the chocolate lands.

     

    At what velocity would the chocolate need to be propelled upwards, if Katherine were to immediately slide down the slide and run to reach the chocolate just as it hits the ground?

     

    Give your answer in `text(ms)^(-1)`, correct to one decimal place.   (2 marks)

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Katherine’s next activity is to ride a mini speedboat. To stop at the correct boat dock, she needs to stop the engine and allow the boat to be slowed by air and water resistance.

At time `t` seconds after the engine has been stopped, the acceleration of the boat, `a\ text(ms)^(-2)`, is related to its velocity, `v\ text(ms)^(-1)`, by

`a = -1/10 sqrt(196-v^2)`.

Katherine stops the engine when the speedboat is travelling at `7\ text(m/s)`.

  1. i.  Find an expression for `v` in terms of `t`.   (3 marks)

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  2. ii. Find the time it takes the speedboat to come to rest.Give your answer in seconds in terms of `pi`.   (2 marks)

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  3. iii. Find the distance it takes the speedboat to come to rest, from when the engine is stopped.Give your answer in metres, correct to one decimal place.   (3 marks)

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Show Answers Only
  1. `10/3\ text(s)`
  2. `2.5\ text(s)`
  3. `35.1\ text(m s)^(−1)`
  4. i.  `v = 14 sin(pi/6-t/10)`
  5. ii. `(5 pi)/3`
  6. iii. `18.8`
Show Worked Solution

a.   `u = 0, quad v = 6, quad s = 10`

COMMENT: Exact form required. 3.3 seconds was marked incorrect!

`text(Solve for)\ \ t:\ \ \ ((u + v)/2)t` `= s`
`((0 + 6)/2)t` `= 10`
`t` `= 10/3\ text(s)`

 

b.   `u = 10, quad a = -9.8, quad s = -6`

COMMENT: Many students showed a “lack of understanding” of displacement here.

`text(Solve for)\ \ t:`

`s` `= ut + 1/2 at^2`
`-6` `= 10t-4.9 t^2`
`:. t` `~~2.5\ text(s)\ \ \ text{(by CAS)}`

♦♦ Mean mark 27%.

c.   `text(Time of chocolate in air)`

`= 10/3 + 4`

`=22/3`
 

`text(Solve for)\ \ u:`

`-6` `= 22/3 u -4.9(22/3)^2`
`:. u` `~~35.1\ text(m s)^(−1)\ \ \ text{(by CAS)}`

 

d.i.    `(dv)/(dt)` `= -1/10 sqrt(196-v^2)`
  `(dt)/(dv)` `= (-10)/sqrt(196-v^2)`
  `t` `= int(-10)/sqrt(196-v^2)\ dv`
  `-t/10` `= int 1/sqrt(14^2-v^2) dv`
  `-t/10` `= sin^(-1)(v/14) + c`

 
`text(When)\ \ t = 0, v = 7`

`=> c=-sin^(-1)(1/2) = -pi/6`
 

`-t/10` `=sin^(-1)(v/14)-pi/6`  
`sin^(-1) (v/14)` `= pi/6-t/10`  
`:. v` `=14sin(pi/6-t/10)`  

 

d.ii.  `text(Find)\ \ t\ \ text(when)\ \ v=0:`

  `-t/10` `=sin^(-1)(0)-pi/6`
  `t` `= -10 sin^(-1)(0) + (10 pi)/6`
    `= (5 pi)/3\ text(s)`

 

d.iii.   `v = 14sin(pi/6-t/10)`

`(dx)/(dt)` `=14sin(pi/6-t/10)`
`x` `= int_0^((5pi)/3)14sin(pi/6-t/10)\ dt`
  `~~ 18.8\ text(m)\ \ \ text{(by CAS)}`

Filed Under: Motion (SM) Tagged With: Band 4, Band 5, smc-1159-10-Motion as f(t), smc-1159-30-a=f(v), smc-1159-50-Projectiles

Vectors, SPEC2 2012 VCAA 4

The position vector of the International Space Station `text{(S)}`, when visible above the horizon from a radar tracking location `text{(O)}` on the surface of Earth, is modelled by

`underset ~r(t) = 6800 sin(pi(1.3t-0.1))underset~i + (6800 cos(pi(1.3t-0.1))-6400)underset ~j`,

for  `t in [0, 0.154]`,

where  `underset ~i`  is a unit vector relative to `text(O)` as shown and  `underset ~j`  is a unit vector vertically up from point `text(O)`. Time  `t`  is measured in hours and displacement components are measured in kilometres.
 

 

  1. Find the height, `h` km, of the space station above the surface of Earth when it is at point `text(P)`, directly above point `text(O)`.
  2. Give your answer correct to the nearest km.   (1 mark)

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  3. Find the acceleration of the space station, and show that its acceleration is perpendicular to its velocity.   (3 marks)

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  4. Find the speed of the space station in km/h.
  5. Give your answer correct to the nearest integer.   (2 marks)

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  6. Find the equation of the path followed by the space station in cartesian form.   (2 marks)

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  7. Find the times when the space station is at a distance of 1000 km from the radar tracking location `text(O)`.
  8. Give your answers in hours, correct to two decimal places.   (3 marks)

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Show Answers Only
  1. `text(400 km)`
  2. `text(See Worked Solutions.)`
  3. `27\ 772\ text(km/h)`
  4. `x^2 + (y + 6400)^2 = 46\ 240\ 000`
  5. `t ~~ 0.04, 0.11`
Show Worked Solution

a.   `text(At)\ \ P,\ \ x(t)=0`

♦ Mean mark 49%.

  `text{Solve (by CAS):}\ \ 6800 sin (pi(1.3t-0.1))` `= 0`

 
`=> t=0.076923…`
 

`:. h` `= 6800 cos (pi (1.3(0.076923)-0.1))-6400`
  `= 400`

 

b.    `underset ~(dot r) (t)` `= 8840pi cos (pi(1.3t-0.1)) underset ~i-8840pi sin (pi(1.3t-0.1)) underset ~j`
  `underset ~(ddot r) (t)` `= -11\ 492 pi^2 sin (pi(1.3t-0.1))underset ~i-11\ 492 pi^2 cos (pi(1.3t-0.1)) underset ~j`

 
`text(Let)\ \ u=pi(1.3t-0.1),`

`underset ~(ddot r) (t) ⋅ underset ~(dot r) (t)` `= -(8840)(11\492) pi^3 cos (u) sin (u) + (8840)(11\492) pi^3 cos(u)sin(u)`

 

  `= 0`

 
`:. underset ~(ddot r) (t) _|_ underset ~(dot r) (t)`

 

c.   `text(Speed)\ = |\ dotr(t)\ |`

♦ Mean mark part (c) 45%.

`|\ dotr(t)\ |` `= sqrt((8840pi)^2 cos^2(pi(1.3t-0.1)) + (8840pi)^2 sin^2 (pi(1.3t-0.1)))`
  `= 8840 pi`
  `~~ 27\ 772`

 

d.    `x/6800` `= sin(pi(1.3t-0.1))`
  `(6400 + y)/6800` `= cos(pi (1.3t-0.1))`

 
`text(Using)\ \ sin^2theta + cos^2theta = 1`

`x^2/6800^2 + (6400 + y)^2/6800^2` `=1`  
`x^2 + (y + 6400)^2` `= 6800^2`  

 

e.  `underset ~r(t) = 6800 sin(u)underset~i + (6800 cos(u)-6400)underset ~j`

♦ Mean mark part (e) 37%.

`text(Find)\ \ t\ \ text(such that)\ \ |\ underset ~r(t)\ | = 1000:`

`6800^2sin^2(u) + (6800 cos(u) -6400)^2 = 1000^2,\ \ \ (u=pi(1.3t-0.1))`

`6800^2-2 xx 6400 xx 6800 cos(u) + 6400^2 = 1000^2`

`=>cos(pi(1.3t-0.1)) = 0.9903\ \ \ text{(by CAS)}`

`:. t=0.04 or 0.11`

Filed Under: Forces and Motion Along a Curve Tagged With: Band 4, Band 5, smc-1179-75-Other applications

Calculus, SPEC2 2012 VCAA 3

A car accelerates from rest. Its speed after `T` seconds is `V\ text(ms)^(−1)`, where

`V = 17 tan^(−1)((pi T)/6), T >= 0`

  1. Write down the limiting speed of the car as  `T -> oo`.   (1 mark)

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  2. Calculate, correct to the nearest `0.1\ text(ms)^(−2)`, the acceleration of the car when  `T = 10`.   (1 mark)

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  3. Calculate, correct to the nearest second, the time it takes for the car to accelerate from rest to `25\ text(ms)^(−1)`.   (2 marks)

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After accelerating to `25\text(ms)^(−1)`, the car stays at this speed for 120 seconds and then begins to decelerate while braking. The speed of the car  `t`  seconds after the brakes are first applied is `v\ text(ms)^(−1)` where

`(dv)/(dt) =-1/100 (145-2t),`

until the car comes to rest.

  1. i.  Find `v` in terms of `t`.   (2 marks)

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  2. ii. Find the time, in seconds, taken for the car to come to rest while braking.   (2 marks)

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  3. i.  Write down the expressions for the distance travelled by the car during each of the three stages of its motion.   (2 marks)

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  4. ii. Find the total distance travelled from when the car starts to accelerate to when it comes to rest.

     

        Give your answer in metres correct to the nearest metre.   (1 mark)

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Show Answers Only
  1. `(17 pi)/2`
  2. `0.3`
  3. `19\ text(s)`
  4. i.  `V = t^2/100-(145 t)/100 + 25`
  5. ii. `t_1 = 20\ text(s)`
  6. i.  `d_1 = int_0^19 17 tan^(-1) ((pi T)/6)\ dT`

     

        `d_2 = 25 xx 120`

     

        `d_3 = int_0^20 -1/100 [145 t-t^2] + 25\ dt`

  7. ii. `3637\ text(m)`
Show Worked Solution

a.   `text(As)\ \ T->oo,\ \ tan^(-1)((piT)/6)->pi/2`

  `:.underset (T->oo) (limV)` `= (17 pi)/2`

 

b.  `(dV)/(dt)= (102 pi)/(36 + pi^2 T^2),\ \ \ text{(by CAS)}`
 

`text(When)\ \ T=10:`

`(dV)/(dt)` `= (102 pi)/(36 + 100 pi^2)`
  `~~ 0.3`

 
c.
   `text(Find)\ \ T\ \ text(when)\ \ V=25:`

  `17 tan^(-1) ((pi T)/6)` `=25 `
  `T` `= 18.995\ \ \ text{(by CAS)}`
    `~~ 19\ text(seconds)`

 

d.i.    `v` `= -1/100 int_0^t 145-2t\ dt`
  `v` `= -1/100 [145 t-t^2] + c`

 
`text(When)\ \ t=0, \ v=25:`

`=> c=25`

`:. v= -1/100 [145 t-t^2] + 25`
 

d.ii.  `text(Find)\ \ t\ \ text(when)\ \ v=0:`

`-1/100[145t-t^2] + 25=0`

`:. t=20\ text(seconds)\ \ \ text{(by CAS)}`

 

e.i.   `text(Stage 1: car travels from rest to 25 m/s)`

`d_1 = int_0^19 17 tan^(-1) ((pi T)/6)\ dT`
  

`text(Stage 2: car travels at 25 m/s for 120 seconds)`

`d_2` `= 25 xx 120`
  `= 3000`

 
`text(Stage 3: car decelerates for 20 seconds`

`d_3 = int_0^20 -1/100 [145 t-t^2] + 25\ dt`

 

e.ii.    `d_1` `~~ 400.131`
  `d_2` `= 3000`
  `d_3` `= 236.6`

 

`text(Total distance)` `= d_1 + d_2 + d_3`
  `~~ 3637\ text(m)`

Filed Under: Motion (SM) Tagged With: Band 3, Band 4, Band 5, smc-1159-10-Motion as f(t)

Complex Numbers, SPEC2 2012 VCAA 2

  1.  Given that  `cos(pi/12) = (sqrt (sqrt 3 + 2))/2`, show that  `sin(pi/12) = (sqrt (2-sqrt 3))/2`.   (2 marks)

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  2. Express  `z_1 = (sqrt(sqrt3 + 2))/2 + i(sqrt(2-sqrt3))/2`  in polar form.   (1 mark)

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  3. i.  Write down  `z_1^4`  in polar form.   (1 mark)

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  4. ii. On the Argand diagram below, shade the region defined by

`{z: text(Arg)(z_1) <= text(Arg)(z) <= text(Arg)(z_1^4)} ∩ {z: 1 <= |\ z\ | <= 2}, z ∈ C`.   (2 marks)

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  1.  Find the area of the shaded region in part c.   (2 marks) 

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  2. i.  Find the value(s) of `n` such that  `text(Re)(z_1^n) = 0`, where  `z_1 = (sqrt(sqrt3 + 2))/2 + i(sqrt(2-sqrt3))/2`.   (3 marks)

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  3. ii. Find  `z_1^n`  for the value(s) of `n` found in part i.   (1 mark)

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Show Answers Only
  1. `text(See Worked Solutions.)`
  2. i.  `z_1 = text(cis) pi/12`

     

    ii.  `z_1^4 = text(cis) pi/3`

  3. `text(See Worked Solutions.)`
  4. `(3pi)/8`
  5. i.  `n = (2k + 1)6`

     

    ii.  `z_1^n = ±i\ text(for)\ k ∈ Z`

Show Worked Solution
a.    `cos^2(pi/12) + sin^2(pi/12)` `= 1`
  `sin^2(pi/12)` `= 1-(sqrt 3 + 2)/4`
    `= (2-sqrt 3)/4`

 
`:. sin (pi/12) = sqrt(2-sqrt 3)/2,\ \ \ (sin (pi/12) > 0)`

 

b.i.    `z_1` `= cos(pi/12) + i sin (pi/12)`
    `= text(cis)(pi/12)`

 

b.ii.    `z_1^4` `= 1^4 text(cis) ((4 pi)/12)`
    `= text(cis)(pi/3)`

 

c.   

 

d.  `text(Area of large sector)`

Mean mark 51%.

`=theta/(2pi) xx pi r^2`

`=(pi/3-pi/12)/(2pi) xx pi xx 2^2`

`=pi/2`
  

`text(Area of small sector)`

`=1/2 xx pi/4 xx 1`

`=pi/8`

 
`:.\ text(Area shaded)`

`= pi/2-pi/8`

`= (3 pi)/8`
 

♦ Mean mark (e)(i) 34%.

e.i.    `z_1^n` `= 1^n text(cis) ((n pi)/12)`
  `text(Re)(z_1^n)` `= cos((n pi)/12) = 0`
  `(n pi)/12` `=cos^(-1)0 +2pik,\ \ \ k in ZZ`
  `(n pi)/12` `= pi/2 + k pi`
  `n` `= 6 + 12k,\ \ \ k in ZZ`

 

e.ii.  `text(When)\ \ n=(6 + 12k):`

♦ Mean mark (e)(ii) 36%.

  `z_1^n` `= 1^(6 + 12k) text(cis) (((6 + 12k)pi)/12), quad k in ZZ`
    `= i xx sin (((6 + 12k)pi)/12)`
    `= i xx sin (pi/2 + k pi)`

 
`text(If)\ \ k=0  or text(even,)\ \ z_1^n=i`

`text(If)\ \ k\ text(is odd,)\ \ z_1^n=-i`

`:. z_1^n = +-i,\ \ \ k in ZZ`

Filed Under: Geometry and Complex Numbers (SM), Mod/Arg Form and Argand Diagrams (SM) Tagged With: Band 3, Band 4, Band 5, smc-1173-30-Sketch regions, smc-2597-20-Cartesian to Mod/Arg, smc-2597-60-Argand diagrams

Mechanics, SPEC2 2012 VCAA 22 MC

A 12 kg mass is suspended in equilibrium from a horizontal ceiling by two identical light strings. Each string makes an angle of 60° with the ceiling, as shown.
 


 

The magnitude, in newtons, of the tension in each string is equal to

A.     `6 g`

B.   `12 g`

C.   `24 g`

D.   `4 sqrt 3 g`

E.   `8 sqrt 3 g`

Show Answers Only

`D`

Show Worked Solution

`T/(sin 30^@)` `= (12 g)/(sin 120^@)`
`2T` `= (24 g)/sqrt3`
`T` `= (12 g)/sqrt3`
  `= 4g sqrt 3`

 
`=> D`

Filed Under: Pulleys, Planes and Equilibrium (SM) Tagged With: Band 4, smc-1175-40-Equilibrium

Vectors, SPEC2 2012 VCAA 17 MC

If  `underset ~u = 2 underset ~i - 2 underset ~j + underset ~k`  and  `underset ~v = 3 underset ~i - 6 underset ~j + 2 underset ~k`, the vector resolute of  `underset ~v`  in the direction of  `underset ~u`  is

A.   `20/49(3 underset ~i - 6 underset ~j + 2 underset ~k)`

B.   `20/3(2 underset ~i - 2underset ~j + underset ~k)`

C.   `20/7(3 underset ~i - 6 underset ~j + 2 underset ~k)`

D.   `20/9(2 underset ~i - 2 underset ~j + underset ~k)`

E.   `1/9(−2 underset ~i + 2 underset ~j - underset ~k)`

Show Answers Only

`D`

Show Worked Solution

`tildeu = 2tildei – 2tildej + tildek,qquadtildev = 3tildei – 6tilde j + 2tildek`

`|\ tildeu\ |` `= sqrt(2^2 + (−2)^2 + 1^2)=3`
`hatu` `= = 1/3(2tildei – 2tildej + tildek)`

 

`tildev*hatu\ \ (text(Scalar resolute of)\ tildev\ text(in the direction of)\ tildeu)`

`= (3tildei – 6tildej + 2tildek)* 1/3(2tildei – 2tildej + tildek)`

`= 20/3`
 

`(tildev*hatu)hatu\ \ (text(Vector resolute of)\ tildev\ text(in the direction of)\ tildeu)`

`= 20/3 xx 1/3(2tildei – 2tildej + tildek)`

`= 20/9(2tildei – 2tildej + tildek)`
 

`=> D`

Filed Under: Basic Concepts and Calculations Tagged With: Band 4, smc-1176-40-Vector resolute

Mechanics, SPEC2 2012 VCAA 14 MC

A particle is acted on by two forces, one of 6 newtons acting due south, the other of 4 newtons acting in the direction N60° W.

The magnitude of the resultant force, in newtons, acting on the particle is

  1. `10`
  2. `2sqrt7`
  3. `2sqrt19`
  4. `sqrt(52 - 24sqrt3)`
  5. `sqrt(52 + 24sqrt3)`
Show Answers Only

`B`

Show Worked Solution

Mean mark 51%.

`x^2` `= 6^2 + 4^2 – 2(6)(4) cos 60^@`
  `= 28`
   
`:. x` `= sqrt 28`
  `= 2 sqrt 7`

 
`=> B`

Filed Under: Pulleys, Planes and Equilibrium (SM) Tagged With: Band 4, smc-1175-20-Horizontal plane

Calculus, SPEC2 2012 VCAA 13 MC

Using a suitable substitution, `int_0^(pi/3) sin^3 (x) cos^4 (x)\ dx`  can be expressed in terms of `u` as

A.   `int_0^(pi/3) (u^6 - u^4)\ du`

B.   `int_1^(1/2) (u^6 - u^4)\ du`

C.   `int_(1/2)^1 (u^6 - u^4)\ du`

D.   `int_0^(sqrt3/2) (u^6 - u^4)\ du`

E.   `int_0^(sqrt3/2) (u^4 - u^6)\ du`

Show Answers Only

`B`

Show Worked Solution

`text(Let)\ \ u = cos(x)`

`(du)/(dx) = -sin(x)\ \ =>\ \ du=-sin(x)\ dx`

`sin^2(x)` `= 1 – cos^2(x)`
  `= 1 – u^2`

 
`text(When)\ \ x = 0, \ u = 1`

`text(When)\ \ x = pi/3, \ u = 1/2`
 

`int_0^(pi/3) sin^3 (x) cos^4 (x)\ dx`

`=-int_1^(1/2) (1 – u^2)u^4\ du`

`= int_1^(1/2) (u^6 – u^4)\ du`

 
`=> B`

Filed Under: Integration by Substitution (SM) Tagged With: Band 4, smc-2564-30-Trig

Calculus, SPEC2 2012 VCAA 11 MC

If  `(d^2y)/(dx^2) = x^2 - x`  and  `(dy)/(dx) = 0`  at  `x = 0`, then the graph of `y` will have

  1. a local minimum at  `x = 1/2`
  2. a local maximum at  `x = 0`  and a local minimum at  `x = 1`
  3. stationary points of inflection at  `x = 0`  and  `x = 1`, and a local minimum at  `x = 3/2`
  4. a stationary points of inflection at  `x = 0`, no other points of inflection and a local minimum at  `x = 3/2`
  5. a stationary point of inflection at  `x = 0`, a non-stationary point of inflection at  `x = 1`  and a local minimum at  `x = 3/2` 
Show Answers Only

`E`

Show Worked Solution

`(d^2y)/(dx^2)=x^2-x`

♦ Mean mark 51%.

`(d^2y)/(dx^2)=0\ \ text(when)\ \ x=0 or 1`

`(dy)/(dx)` ` = (x^3)/3 – (x^2)/2 + c`
  `= x^2(x/3 – 1/2) + c`

 
`text(Given)\ \ (dy)/(dx) = 0\ \ text(when)\ \ x = 0\ \ =>\ \ c=0`

`(dy)/(dx) = 0\ \ text(when)\ \ x = 0 or 3/2`

`(d^2y)/(dx^2)|_(x = 3/2) = 3/4>0`

`:.\ text(Local minimum at)\ \ x = 3/2`
 

`text(At)\ \ x=0, dy/dx<0\ \ text(either side)`

`:.\ text(Stationary point of inflection at)\ x=0`

`text(At)\ \ x=1, \ dy/dx!=0, \ dy/dx<0\ \ text(either side)`

`:.\ text(Non-stationary point of inflection at)\ \ x = 1`

`=> E`

Filed Under: Tangents and Curve Sketching Tagged With: Band 4, smc-1182-40-Other 1st/2nd deriv problems

Calculus, SPEC2 2012 VCAA 10 MC

The diagram that best represents the direction field of the differential equation  `(dy)/(dx) = xy`  is

A. B.
C. D.
Show Answers Only

`A`

Show Worked Solution

`(dy)/(dx) = xy`

`text(When)\ \ x=0 \ or\  y=0\ \ =>\ text(gradient = 0)`

`text(In 1st and 3rd quartile)\ \ =>\ \ text(gradients positive)`

`text(In 2nd and 4th quartile)\ \ =>\ \ text(gradients negative)`

`=> A`

Filed Under: Euler, Pseudocode and Slope Fields Tagged With: Band 4, smc-1183-20-Slope fields

Calculus, SPEC2 2012 VCAA 9 MC

Euler's formula is used to find  `y_2`, where  `(dy)/(dx) = cos(x),\ x_0 = 0, \ y_0 = 1`  and  `h = 0.1`.

The value of `y_2` correct to four decimal places is

A.   1.1000 and this is an underestimate of  `y(0.2)`

B.   1.1995 and this is an overestimate of  `y(0.2)`

C.   1.1995 and this is an underestimate of  `y(0.2)`

D.   1.2975 and this is an underestimate of  `y(0.2)`

E.   1.2975 and this is an overestimate of  `y(0.2)`

Show Answers Only

`B`

Show Worked Solution

`x_0 = 0,\ \ y_0 = 1,\ \ h=0.1`

`y_1` `= y_0 + h* (dy)/(dx)|_{(0,1)}`
  `= 1 + 0.1 xx cos(0)`
  `= 1.1`
   
`y_2` `= 1.1 + 0.1 xx cos(0.1)`
  `~~ 1.1995`

 
`text(S)text(ince)\ \ sin(x)\ \ text(is concave down in the region)\ \ x=0.2,`

`1.1995\ text(is an overestimate.)`

`=> B`

Filed Under: Euler, Pseudocode and Slope Fields Tagged With: Band 4, smc-1183-10-Euler method

Calculus, SPEC2 2011 VCAA 22 MC

A particle moves in a straight line. At time  `t`  seconds, where  `t >= 0`, its displacement `x` metres from the origin and its velocity  `v`  metres per second are such that  `v = 25 + x^2`.

If  `x = 5`  initially, then  `t`  is equal to

  1. `25x + (x^3)/3`
  2. `25x + (x^3)/3 - 500/3`
  3. `1/5tan^(−1)(x/5) + 5`
  4. `tan^(−1)(x/5) - pi/4`
  5. `1/5tan^(−1)(x/5) - pi/20`
Show Answers Only

`E`

Show Worked Solution

`(dx)/(dt) = 25 + x^2`

`(dt)/(dx) = 1/(25 + x^2)`

`t` `= int 1/(25 + x^2)\ dx`
  `= 1/5 int 5/(5^2 + x^2)\ dx`
  `= 1/5 tan^(−1)(x/5) + c`

 
`text(When)\ \ t=0,\ \ x=5:`

`0` `= 1/5 tan^(−1)(5/5) +c`
`c` `= – pi/20`

 
`:. t= 1/5 tan^(−1)(x/5) – pi/20`

`=> E`

Filed Under: Motion (SM) Tagged With: Band 4, smc-1159-20-Motion as f(x)

Calculus, SPEC2 2011 VCAA 20 MC

A body moves in a straight line such that its velocity  `v\ text(ms)^(-1)`  is given by  `v = 2sqrt(1 - x^2)`, where `x` metres is its displacement from the origin.

The acceleration of the body in `text(ms)^(-2)`  is given by

  1. `(−2x)/(sqrt(1 - x^2))`
  2. `−2x`
  3. `2/(sqrt(1 - x^2))`
  4. `2(1 - 2x)`
  5. `−4x`
Show Answers Only

`E`

Show Worked Solution

`v = 2(sqrt(1 – x^2))`

`a` `=v *(dv)/(dx)`  
  `= 2sqrt(1 – x^2) xx 2 xx (−2x) xx 1/(2sqrt(1 – x^2))`  
  `= −(4x sqrt(1 – x^2))/sqrt( 1 – x^2)`  
  `= −4x`  

  
`=> E`

Filed Under: Motion (SM) Tagged With: Band 4, smc-1159-20-Motion as f(x)

Calculus, SPEC2 2011 VCAA 19 MC

The motion of a lift (elevator) in a shopping centre is given by the velocity-time graph below, where time  `t`  is in seconds, and the velocity of the lift is `v` metres per second. For  `v > 0`  the lift is moving upwards.
 

SPEC2 2011 VCAA 19 MC
 

The graph shows that at the end of 30 seconds, the position of the lift is

A.   17.5 metres above its starting level.

B.   5 metres above its starting level.

C.   at the same position as its starting level.

D.   5 metres below its starting level.

E.   17.5 metres below its starting level.

Show Answers Only

`A`

Show Worked Solution
`text(Distance)` `= text(Area of trap) – text(Area of triangle)`
  `= 1/2(5 + 15)3 – 1/2 xx 10 xx 2.5`
  `= 17.5\ text(m)`

 
`text{Net area is above the}\ xtext{-axis (lift is higher).}`

`=> A`

Filed Under: Motion (SM) Tagged With: Band 4, smc-1159-40-Graphs

Calculus, SPEC2 2011 VCAA 18 MC

The amount of chemical `x` in a tank at time  `t`  is given by the differential equation  `dx/dt = -10/(10 - t)`  and when  `t = 0`, `\ x_0 = 5`. Euler's method is used with a step size of 0.5 in the values of  `t`.

The value of `x` correct to two decimal places when  `t = 1`  is found to be

A.   3.95

B.   3.97

C.   4.50

D.   5.50

E.   6.03

Show Answers Only

`B`

Show Worked Solution
`x_1 ~~ x(0.5)` `= 5 + 0.5 xx (−10/(10 – 0))`
  `= 5 – 0.5`
  `= 4.5`

 

Mean mark 51%.

`x_2 ~~ x(1)` `= 4.5 + 0.5 xx (−10/(10 – 0.5))`
  `= 4.5 – 10/19`
  `~~ 3.97`

`=> B`

Filed Under: Euler, Pseudocode and Slope Fields Tagged With: Band 4, smc-1183-10-Euler method

Calculus, SPEC2 2011 VCAA 17 MC

SPEC2 2011 VCAA 17 MC

The differential equation which best represents the above direction field is

A.   `(dy)/(dx) = (y - 2x)/(2y + x)`

B.   `(dy)/(dx) = (2x - y)/(y - 2x)`

C.   `(dy)/(dx) = (2y - x)/(y + 2x)`

D.   `(dy)/(dx) = (y - 2x)/(2y - x)`

E.   `(dy)/(dx) = (x - 2y)/(2y + x)`

Show Answers Only

`A`

Show Worked Solution

`text(When)\ \ x=0\ \ => \ \ text(gradients are all positive)`

Almost half of all students answered incorrectly – mean mark 52%.

`text(Eliminate B and E.)`

`text(When)\ \ y=0\ \ => \ \ text(gradients are all negative)`

`text(Eliminate D.)`

`text(Option A will have zero gradient along)\ \ y=2x\ \ text{(correct)}`

`text(Option C will have zero gradient along)\ \ y=1/2 x\ \ text{(incorrect)}`

`=> A`

Filed Under: Euler, Pseudocode and Slope Fields Tagged With: Band 4, smc-1183-20-Slope fields

Calculus, SPEC2 2011 VCAA 15 MC

Using a suitable substitution, the definite integral  `int_0^(pi/24)tan(2x)sec^2(2x)\ dx`  is equivalent to

A.   `1/2int_0^(pi/24)(u)\ du`

B.   `2int_0^(pi/24)(u)\ du`

C.   `int_0^(2 - sqrt3)(u)\ du`

D.   `1/2int_0^(2 - sqrt3)(u)\ du`

E.   `2int_0^(2 - sqrt3)(u)\ du`

Show Answers Only

`D`

Show Worked Solution

`text(Let)\ \ u = tan(2x)`

`(du)/dx = 2 sec^2(2x)\ \ =>\ \ 1/2 du = sec^2(2x)\ dx`
 

`text(When)\ \ x=pi/24\ \ =>\ \ u=tan(pi/12)=2-sqrt3\ \ text{(by CAS)}`

`text(When)\ \ x=0\ \ =>\ \ u=0`
 

`:. int_0^(pi/24)tan(2x)sec^2(2x)\ dx`

`= 1/2int_0^(2 – sqrt3)(u)\ du`

`=> D`

Filed Under: Integration by Substitution (SM) Tagged With: Band 4, smc-2564-30-Trig

Calculus, SPEC2 2011 VCAA 14 MC

If  `f″(x) = 2e^xsin(x)`,  `f′(0) = 0`  and  `f(0) = 0`, the  `f(x)`  equals

A.   `−e^x(cos(x) + sin(x))`

B.   `−e^x(cos(x) - sin(x)) + 1`

C.   `−e^xcos(x)`

D.   `x - e^xcos(x) + 1`

E.   `x - e^xcos(x)`

Show Answers Only

`D`

Show Worked Solution

`text(Consider:)\ \ f(0)=0,`

`=>\ text(Eliminate A, C and E.)`

`text(By CAS, B and D satisfy)\ \ f′(0) = 0.`

`text(By CAS, only D satisfies)\ \ f″(x) = 2e^x sin(x)`

`=> D`

Filed Under: Arc Lengths, Areas and Other Tagged With: Band 4, smc-1181-30-Other

Vectors, SPEC2 2011 VCAA 13 MC

The position of a particle at time  `t`  is given by  `underset~r(t) = (sqrt(t - 2))underset~i + (2t)underset~j`  for  `t >= 2`.

The cartesian equation of the path of the particle is

A.   `y = 2x^2 + 4`, `x >= 2`
B.   `y = 2x^2 + 2`, `x >= 2`
C.   `y = 2x^2 + 4`, `x >= 0`
D.   `y = sqrt((x - 4)/2)`, `x >= 4`
E.   `y = 2x^2 + 2`, `x >= 0`

 

Show Answers Only

`C`

Show Worked Solution

`tilder(t) = (sqrt(t – 2)tildei + (2t)tildej)`

`x = sqrt(t – 2)`

`text(Given)\ \ t >= 2\ \ =>\ \ x >=0`

`y = 2t\ \ =>\ \ t = y/2`

`:. x` `= sqrt(y/2 – 2)`
`x^2` `= y/2 – 2`
`y/2` `= x^2 + 2`
`y` `= 2x^2 + 4`

 
`=> C`

Filed Under: Position Vectors as a Function of Time Tagged With: Band 4, smc-1178-10-Find Cartesian equation

Vectors, SPEC2 2011 VCAA 11 MC

Consider the three forces

`underset~F_1 = −sqrt3underset~j`,  `underset~F_2 = underset~i + sqrt3underset~j`  and  `underset~F_3 = −1/2underset~i + sqrt3/2underset~j`.

The magnitude of the sum of these three forces is equal to

  1. the magnitude of `(underset~F_3 - underset~F_1)`
  2. the magnitude of `(underset~F_2 - underset~F_1)`
  3. the magnitude of `underset~F_1`
  4. the magnitude of `underset~F_2`
  5. the magnitude of `underset~F_3`
Show Answers Only

`E`

Show Worked Solution
`underset~(F_1) + underset~(F_2) + underset~(F_3)` `= (1 – 1/2)underset~i + (−sqrt3 + sqrt3 + sqrt3/2)underset~j`
  `= 1/2 underset~i + sqrt3/2underset~j`
`|underset~(F_1) + underset~(F_2) + underset~(F_3)|` `= sqrt((1/2)^2 + (sqrt3/2)^2)`
  `= |underset~(F_3)|`

`=> E`

Filed Under: Forces and Motion Along a Curve Tagged With: Band 4, smc-1179-10-Force magnitude

Vectors, SPEC2 2011 VCAA 10 MC

The diagram below shows a rhombus, spanned by the two vectors  `underset~a`  and  `underset~b`.
 

SPEC2 2011 VCAA 10 MC
 

It follows that

A.   `underset~a.underset~b = 0`

B.   `underset~a = underset~b`

C.   `(underset~a + underset~b).(underset~a - underset~b) = 0`

D.   `|\ underset~a + underset~b\ | = |\ underset~a - underset~b|`

E.   `2underset~a + 2underset~b = underset~0`

Show Answers Only

`C`

Show Worked Solution

`text(Consider A:)`

`text(If)\ \ underset~a · underset~b = 0\ \ =>\ \ underset~a ⊥ underset~b\ \ text{(incorrect)}`

`text(Consider B:)`

`underset~a != underset~b\ \ text{(incorrect)}`

`text(Consider C:)`

`underset~a + underset~b` `= overset(->)(OC)`
`underset~a – underset~b` `= overset(->)(BA)`

 
`overset(->)(OC) · overset(->)(BA)=0`

`text{The diagonals of a rhombus are perpendicular  (correct)}`

`=> C`

Filed Under: Vector Lines, Planes and Geometry Tagged With: Band 4, smc-1177-30-Quadrilaterals, smc-1177-50-2D problems

Complex Numbers, SPEC2 2011 VCAA 7 MC

In the complex plane, the circle with equation  `|\ z - (2 + 3i)\ | = 1`  is intersected exactly twice by the curve with equation

A.   `|\ z - 3i\ | = 1`

B.   `|\ z + 3\ | = |\ z - 3i\ |`

C.   `|\ z - 3\ | = |\ z - 3i\ |`

D.   `text(Im)(z) = 4`

E.   `text(Re)(z) = 3`

Show Answers Only

`C`

Show Worked Solution

`text(Consider option C:)`

`|z – 3| = |z – 3i|`

`=> y = x\ text{(perpendicular bisector}`

`text{between (3, 0) and (0, 3)}`
 

`=> C`

Filed Under: Geometry and Complex Numbers (SM) Tagged With: Band 4, smc-1173-10-Circles, smc-1173-40-Linear

Complex Numbers, SPEC2 2011 VCAA 6 MC

The polynomial `P(z)` has real coefficients. Four of the roots of the equation  `P(z) = 0`  are  `z = 0`,  `z = 1 - 2i`,  `z = 1 + 2i`  and  `z = 3i`.

The minimum number of roots that the equation  `P(z) = 0`  could have is

A.   4

B.   5

C.   6

D.   7

E.   8

Show Answers Only

`B`

Show Worked Solution

`P(z) = 0\ text(has real coefficients,)`

`=>\ text(Conjugate root theorem applies)`

`z = −3i\ \ text(is also a root)`

`:.\ text(Minimum roots = 5)`

`=> B`

Filed Under: Factors and Roots (SM) Tagged With: Band 4, smc-1172-30-Roots > 3

Complex Numbers, SPEC2 2011 VCAA 5 MC

A certain complex number `z`, where `|\ z\ | > 1`, is represented by the point on the following argand diagram.
 

SPEC2 2011 VCAA 5 MC
 

All axes below have the same scale as those in the diagram above.

The complex number  `1/barz`  is best represented by

SPEC2 2011 VCAA 5 MC ab

SPEC2 2011 VCAA 5 MC cd

SPEC2 2011 VCAA 5 MC e

Show Answers Only

`C`

Show Worked Solution

`|z| > 1`

`|1/(barz)| < 1`

`1/(barz)` `= 1/(x – iy) xx (x + iy)/(x + iy)`
  `= (x + iy)/(x^2 + y^2)`
  `= z/(|z|^2)`

 
`:.\ 1/barz\ \ text(has same argument as)\ z,\ text(smaller magnitude.)`

`=> C`

Filed Under: Geometry and Complex Numbers (SM) Tagged With: Band 4, smc-1173-60-Other

Calculus, SPEC1 2011 VCAA 11

The region in the first quadrant enclosed by the curve  `y = sin(x)`, the line  `y = 0`  and the line  `x = pi/6`  is rotated about the `x`-axis.

Find the volume of the resulting solid of revolution.   (3 marks)

--- 8 WORK AREA LINES (style=lined) ---

Show Answers Only

`pi^2/12-(sqrt3 pi)/8\ \ text(u³)`

Show Worked Solution

`V` `= pi int_(0)^(pi/6) y^2\ dx`
  `= pi int_0^(pi/6) sin^2(x)\ dx`
  `= pi/2 int_0^(pi/6) (1-cos 2x)\ dx`
  `= pi/2 [x-1/2 sin (2x)]_0^(pi/6)`
  `=pi/2 [(pi/6-1/2 sin (pi/3))-0]`
  `=pi/2 (pi/6-(sqrt 3)/4)`
  `=pi^2/12-(sqrt3 pi)/8\ \ text(u³)`

Filed Under: Solids of Revolution Tagged With: Band 4, smc-1180-20-Trig function, smc-1180-50-x-axis rotations

Calculus, SPEC2 2012 VCAA 18 MC

The velocity–time graph for the first 2 seconds of the motion of a particle that is moving in a straight line with respect to a fixed point is shown below.

 

The particle’s velocity `v` is measured in cm/s. Initially the particle is  `x_0` cm from the fixed point.

The distance travelled by the particle in the first 2 seconds of its motion is given by

A.   `int_0^2 v\ dt`

B.   `int_0^2 v\ dt + x_0`

C.   `int_1^2 v\ dt - int_0^1 v\ dt`

D.   `|\ int_0^2 v\ dt\ |`

E.   `int_1^2 v\ dt - int_0^1 v\ dt + x_0`

Show Answers Only

`C`

Show Worked Solution

`text(Distance = Total area between curve and the axis)`

COMMENT: Starting point `x_0` has no effect on total distance travelled.

`d= int_1^2 v\ dt – int_0^1 v\ dt`

 
`=> C`

Filed Under: Motion (SM) Tagged With: Band 4, smc-1159-40-Graphs

Vectors, SPEC1 2011 VCAA 9

Consider the three vectors

`underset ~a = underset ~i - underset ~j + 2underset ~k,\ underset ~b = underset ~i + 2 underset ~j + m underset ~k`  and  `underset ~c = underset ~i + underset ~j - underset ~k`, where `m in R.`

  1. Find the value(s) of `m` for which  `|\ underset ~b\ | = 2 sqrt 3.`  (2 marks)

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  2. Find the value of `m` such that  `underset ~a`  is perpendicular to  `underset ~b.`  (1 mark)

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  3. i.  Calculate  `3 underset ~c - underset ~a.`  (1 mark)

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  4. ii. Hence find a value of `m` such that  `underset ~a, underset ~b`  and  `underset ~c`  are linearly dependent.  (1 mark)

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Show Answers Only

  1. `+- sqrt 7`
  2. `1/2`
  3. i.  `2 tilde i + 4 tilde j – 5 tilde k`
  4. ii. `-5/2`

Show Worked Solution

a.    `|underset~b|` `= sqrt(1^2 + 2^2 + m^2)` `= 2sqrt3`
    `1 + 4 + m^2` `= 4 xx 3`
    `m^2` `= 7`
    `m` `= ±sqrt7`

 

b.    `underset~a * underset~b` `= 1 xx 1 + (−1) xx 2 + 2 xx m`  
  `0` `= 1 – 2 + 2m\ \ ( underset~a ⊥ underset~b)`  
  `2m` `= 1`  
  `m` `= 1/2`  

 

c.i.   `3 underset ~c – underset ~a`

`=3underset~i – underset~i + 3underset~j + underset~j -3underset~k – 2underset~k`

`=2underset~i + 4underset~j-5underset~k`

 

c.ii.   `text(Linear dependence)\ \ =>\ \ 3underset~c – underset~a = t underset~b,\ \ t in RR`

`2 tilde i + 4 tilde j – 5 tilde k= t (tilde i + 2 tilde j + m tilde k)`

`=> t = 2 and tm = -5,`

`:. m=-5/2`

Filed Under: Basic Concepts and Calculations Tagged With: Band 3, Band 4, smc-1176-30-Perpendicular vectors, smc-1176-50-Linear dependence

Mechanics, SPEC1 2011 VCAA 7

A flowerpot of mass `m` kg is held in equilibrium by two light ropes, both of which are connected to a ceiling. The first rope makes an angle of 30° to the vertical and has tension `T_1` newtons. The second makes an angle of 60° to the vertical and has tension `T_2` newtons.
 

VCAA 2011 spec 7b
 

  1. Show that `T_2 = T_1/sqrt 3.`  (1 mark)
  2. The first rope is strong, but the second rope will break if the tension in it exceeds 98 newtons.

     

    Find the maximum value of `m` for which the flowerpot will remain in equilibrium.  (3 marks)

Show Answers Only
  1. `text(Proof)\ \ text{(See Worked Solutions)}`
  2. `m = 20\ text(kg)`
Show Worked Solution

a.   `text(Forces in equilibrium:)`

`tan 30^@` `=T_2/T_1`
`T_2` `= T_1 xx tan30^@`
`T_2` `= T_1/sqrt3\ \ text(.. as required)`

 

b.    `sin30^@` `= (T_2)/(mg)`
  `T_2` `= (mg)/2`
  `98` `=(m_text(max) xx 9.8)/2`
  `m_text(max)` `=(2 xx 98)/9.8`
    `=20\ text(kg)`

Filed Under: Pulleys, Planes and Equilibrium (SM) Tagged With: Band 4, smc-1175-40-Equilibrium

Calculus, SPEC1 2011 VCAA 6

Evaluate  `int_0^1 e^x cos (e^x)\ dx.`  (2 marks)

Show Answers Only

`sin(e) – sin (1)`

Show Worked Solution

`text(Let)\ \ u = e^x`

`(du)/(dx) = e^x\ \ =>\ \ du=e^x\ dx`

`text(When)\ \ x=1,\ \ u=e`

`text(When)\ \ x=0,\ \ u=^0=1`
 

`:. int_0^1 e^xcos(e^x)\ dx` `= int_1^e cos(u)\ du`
  `= [sin(u)]_1^e`
  `= sin (e) – sin1`

Filed Under: Integration by Substitution (SM) Tagged With: Band 4, smc-2564-40-Logs and exponentials

Calculus, SPEC1 2011 VCAA 5

For the curve with parametric equations

`x = 4 sin (t) - 1`

`y = 2 cos (t) + 3`

Find  `(dy)/(dx)`  at the point  `(1, sqrt 3 + 3).`  (3 marks)

Show Answers Only

`– sqrt 3/6`

Show Worked Solution

`(dx)/(dt) = 4cos(t)`

`(dy)/(dt) = −2sin(t)`

`(dy)/(dx)` `= ((dy)/(dt))/((dx)/(dt))`
  `= (-sin t)/(2cos t)`

 
`x = 4 sin (t) – 1\ \ text{(given)}\ \ =>\ \ sin(t)=(x+1)/4`

`y = 2 cos (t) + 3\ \ text{(given)}\ \ =>\ \ 2cos(t)=(y-3)`

`=> dy/dx= (-(x + 1)/4)/(y – 3)`
 

`text(At)\ \ (1, sqrt 3 + 3):`

`:. (dy)/(dx)` `= (-1/2)/(sqrt3+3 -3)`
  `= -1/(2sqrt3)`
  `= – sqrt3/6`

Filed Under: Tangents and Curve Sketching Tagged With: Band 4, smc-1182-10-Find gradient, smc-1182-65-Paramatric functions

Complex Numbers, SPEC2 2012 VCAA 8 MC

If  `z = a + bi`, where both `a` and `b` are non-zero real numbers and  `z in C`, which of the following does not represent a real number?

  1. `z + barz`
  2. `|\ z\ |`
  3. `zbarz`
  4. `z^2-2abi`
  5. `(z-bar z) (z + bar z)`
Show Answers Only

`E`

Show Worked Solution

`text(Consider each option:)`

`text(A.) quad a + bi + a-bi = 2a`  ✔

`text(B.) quad sqrt(a^2 + b^2)`  ✔

`text(C.) quad (a + bi) (a-bi) = a^2 + b^2`  ✔

`text(D.) quad (a + bi)^2-2abi`

`= a^2 +2abi-b^2-2abi`

`= a^2-b^2`  ✔

`text(E.) quad (a + bi-(a-bi))((a + bi + a-bi))`

`= (2bi) (2a)`

`= 4abi`  ✖

 
`=> E`

Filed Under: Basic Calculations (SM) Tagged With: Band 4, smc-1171-10-Basic Calculations

Complex Numbers, SPEC2 2012 VCAA 7 MC

The set of points in the complex plane defined by  `|\ z + 2i\ | = |\ z\ |`  corresponds to

A.   the point given by  `z = −i`

B.   the line  `text(Im)(z) = −1`

C.   the line  `text(Im)(z) = −i`

D.   the line  `text(Re)(z) = −1`

E.   the circle with centre  `−2i`  and radius `1`

Show Answers Only

`B`

Show Worked Solution

`|\ z + 2i\ | = |\ z\ |\ \ =>\ \  |\ z – (−2i)\ | = |\ z\ |`

`text{Find all points equidistant from (0, −2) and (0, 0):}`

`text(Midpoint):\ ((0 + 0)/2, (0 – 2)/2) = (0, -1)`

`m= (-2 – 0)/(0 – 0) = oo`

`:. m_(_|_) = 0\ \ text{(i.e. horizontal line)}`

`:. y = -1 \ \ or\ \ text{Im} (z) = -1`

 
`=> B`

Filed Under: Geometry and Complex Numbers (SM) Tagged With: Band 4, smc-1173-40-Linear

Complex Numbers, SPEC2 2012 VCAA 5 MC

If  `z = sqrt 2 text(cis)(-(4 pi)/5)`  and  `w = z^9`, then

A.   `w = 16 sqrt 2 text(cis)((36 pi)/5)`

B.   `w = 16 sqrt 2 text(cis)(−pi/5)`

C.   `w = 16 sqrt 2 text(cis)((4pi)/5)`

D.   `w = 9 sqrt 2 text(cis)(-pi/5)`

E.   `w = 9 sqrt 2 text(cis)((4pi)/5)`

Show Answers Only

`C`

Show Worked Solution

`z = sqrt2 text(cis) (−(4pi)/5)`

`text(By De Moivre:)`

`w` `= z^9`
  `= (sqrt 2)^9 text(cis)(-(4pi)/5 xx 9)`
  `= 16 sqrt2 text(cis)(-(36pi)/5)`
  `= 16 sqrt 2 text(cis)((4pi)/5 – 8pi)`
  `= 16 sqrt 2 text(cis)((4pi)/5)`

 
`=> C`

Filed Under: Mod/Arg Form and Argand Diagrams (SM) Tagged With: Band 4, smc-2597-50-Mod/Arg and powers

Calculus, SPEC1 2011 VCAA 3

  1. Show that  `f(x) = (2x^2 + 3)/(x^2 + 1)`  can be written in the form  `f(x) = 2 + 1/(x^2 + 1).`  (1 mark)

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  2. Sketch the graph of the relation  `y = (2x^2 + 3)/(x^2 + 1)`  on the axes below.
  3. Label any asymptotes with their equations and label any intercepts with the axes, writing them as coordinates.  (3 marks)

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    VCAA 2011 spec 3b
     

  4. Find the area enclosed by the graph of the relation  `y = (2x^2 + 3)/(x^2 + 1)`, the `x`-axis, and the lines  `x = -1`  and  `x = 1.`  (3 marks)

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Show Answers Only

  1. `text(Proof)\ \ text{(See Worked Solutions)}`
  2. “
    VCAA 2011 spec 3bi
  3. `4 + pi/2`

Show Worked Solution

a.    `f(x)` `= (2x^2 + 3)/(x^2 + 1)`
    `= (2(x^2 + 1) + 1)/(x^2 + 1)`
    `= 2 + 1/(x^2 + 1)`

 

b.   `underset (x→oo) (lim y) = 2`

`text(S)text(ince)\ \ x^2>0\ \ text(for all)\ x,`

`=> f(x)_text(max)\ \ text(occurs when)\ \ x=0\ \ text(at)\ \ (0,3)`
 

VCAA 2011 spec 3bi

 

c.   `f(x)\ \ text(is an even function.)`

`:.\ text(Area)` `= 2 int_0^1 2 + 1/(x^2 + 1)\ dx`  
  `= 2[2x + tan^(−1)(x)]_0^1`  
  `=2[(2+pi/4)-0]`  
  `= 4 + pi/2`  

Filed Under: Arc Lengths, Areas and Other Tagged With: Band 2, Band 4, smc-1181-20-Area Under Curves

Calculus, SPEC1 2011 VCAA 2

Find the value of the real constant `k` given that  `kxe^(2x)`  is a solution of the differential equation

`(d^2y)/(dx^2)-2 (dy)/(dx) + 5y = e^(2x) (15x + 6).`  (3 marks)

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Show Answers Only

`k = 3`

Show Worked Solution
`y` `=kxe^(2x)`
`(dy)/(dx)` `= ke^(2x) + kx(2e^(2x))`
  `= ke^(2x)(1 + 2x)`

 

`(d^2 y)/(dx)` `= 2ke^(2x)(1 + 2x) + 2ke^(2x)`
  `= 2ke^(2x)(1 + 2x + 1)`
  `= 4ke^(2x)(1 + x)`

 

`e^(2x)(15x + 6)` `= (d^2 y)/(dx^2)-2(dy)/(dx) + 5y`
`e^(2x)(15x + 6)` `= 4ke^(2x) + 4kxe^(2x)-2ke^(2x)-4kxe^(2k) + 5kxe^(2x)`
`e^(2x)(15x + 6)` `= 2ke^(2x) + 5kxe^(2x)`
` e^(2x)(15x + 6)` `=e^(2x)(5kx + 2k)`

 
`=> 5kx = 15x, \ \ 2k = 6`

`:. k = 3`

Filed Under: Equations Tagged With: Band 4, smc-5161-10-1st/2nd deriv equations

Calculus, SPEC1 2011 VCAA 1

Find an antiderivative of  `(1 + x)/(9-x^2),\ \ x in R \ text(\{– 3, 3}).`  (3 marks)

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Show Answers Only

`-1/3ln((3-x)^2(|3 + x|))`

Show Worked Solution
`int (1 + x)/(9-x^2)\ dx` `= int (1-x)/((3-x)(3 + x))\ dx`
  `= int A/(3-x) + B/(3 + x)\ dx`

 
`text(Using partial fractions:)`

`A(3 + x) + B(3-x) = 1 + x`

`text(When)\ \ x=3, \ 6A=4\ \ =>\ \ A=2/3`

`text(When)\ \ x=-3, \ 6B=-2\ \ =>\ \ B=-1/3`
 

`:. int (1 + x)/(9-x^2)\ dx`

`int 2/3 (1/(3-x))-1/3 (1/(3 + x))\ dx`

`= -2/3ln|3-x|-1/3ln|3 + x|,\ \ \ (c=0)`

Filed Under: Partial Fractions and Other Integration (SM) Tagged With: Band 4, smc-2565-10-Quadratic denom, smc-2565-60-PF not given

Graphs, SPEC2 2012 VCAA 3 MC

The graph of  `y = f(x)`  is shown below.
 

All the axes below have the same scale as the axes in the diagram above.

The graph of  `y = 1/(f(x))`  is best represented by

A.    B.   
C.    D.   
E.       

Show Answers Only

`E`

Show Worked Solution

`y(-1) = 0`

`-> 1/(y(-1)):\ text(asymptote)\ x = -1`

`text(Eliminate A and B.)`

`text(Local max at)\ \ x = 1`

`-> 1/(y(1)):\ text(local min)`
 

`=> E`

Filed Under: Partial Fractions, Quotient and Other Functions (SM) Tagged With: Band 4, smc-1154-10-Quotient functions/Asymptotes

Graphs, SPEC1 2012 VCAA 10

Consider the functions with rules  `f(x) = arcsin (x/2) + 3/sqrt (25 x^2-1)`  and  `g(x) = arcsin (3x)-3/sqrt (25x^2-1).`

    1. Find the maximal domain of  `f_1(x) = arcsin (x/2).`   (1 mark)

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    2. Find the maximal domain of  `f_2(x) = 3/sqrt (25x^2-1).`   (1 mark)

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    3. Find the largest set of values of  `x in R`  for which  `f(x)`  is defined.   (1 mark)

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  1. Given that  `h(x) = f(x) + g(x)`  and that  `theta = h(1/4)`, evaluate  `sin (theta).`

     

    Give your answer in the form  `(a sqrt b)/c, \ a, b, c in Z.`   (3 marks)

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    1. `-2 <= x <= 2`
    2. `x < -1/5 uu x > 1/5`
    3. `-2 <= x < -1/5 uu 1/5 < x <= 2`
  1. `(5 sqrt 7)/16`
Show Worked Solution

a.i.   `text(Maximal Domain occurs when:)`

  `-1 <= x/2 <= 1`
  `{x: -2 <= x <= 2}`

 
a.ii.
   `text(Maximal Domain occurs when:)`

♦♦ Mean mark part (a)(ii) 33%.

  `25x^2-1 > 0`
  `x^2 > 1/25`
  `{x: x < -1/5 uu x > 1/5}`

 

a.iii.  `text(Max domain for which)\ \ f(x)\ \ text(is defined:)`

♦♦ Mean mark part (a)(iii) 26%.

  `(-2 <= x <= 2) nn (x < -1/5 uu x > 1/5)`
  `{x: -2 <= x < -1/5 \ uu \ 1/5 < x <= 2}`

 

b.    `h(x)` `= sin^(-1) (x/2) + 3/sqrt(25x^2-1) + sin^(-1)(3x)-3/sqrt(25x^2-1)`
    `= sin^(-1)(x/2) + sin^(-1)(3x)`

 
`text(When)\ \ x=1/4,\ \ h(x)=theta`

♦♦♦ Mean mark part (b) 20%.

`theta=sin^(-1) (1/8) + sin^(-1) (3/4)`

`text(Let)\ \ theta_1 = sin^(-1) (1/8),\ \ theta_2 = sin^(-1) (3/4)`

`text(Using)\ \ sin(theta_1 + theta_2)=sin theta_1 cos theta_2 + cos theta_1 sin theta_2:`

`sin(theta)` `= 1/8 * sqrt7/4 + sqrt63/8 * 3/4`
  `=sqrt7/32 + (9sqrt7)/32`
  `=(5 sqrt7)/16`

Filed Under: Inverse Trig Functions (SM) Tagged With: Band 4, Band 5, Band 6, smc-1153-10-arcsin

Vectors, SPEC1 2012 VCAA 9

The position of a particle at time  `t`  is given by

`underset ~r (t) = (2 sqrt (t^2 + 2) - t^2) underset ~i + (2 sqrt (t^2 + 2) + 2t) underset ~j,\ \ t >= 0.`

  1. Find the velocity of the particle at time  `t.`   (1 mark)

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  2. Find the speed of the particle at time  `t = 1`  in the form  `(a sqrt b)/c`, where `a, b` and `c` are positive integers.   (2 marks)

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  3. Show that at time  `t = 1,\ \ (dy)/(dx) = (1 + sqrt 3)/(1 - sqrt 3).`   (2 marks)

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  4. Find the angle in terms of `pi`, between the vector  `-sqrt 3 underset ~i + underset ~j`  and the vector  `underset ~r (t)`  at time  `t = 0.`   (2 marks)

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Show Answers Only
  1. `((2t)/sqrt(t^2 + 2) – 2t) underset ~i + ((2t)/sqrt(t^2 + 2) + 2) underset ~j`
  2. `(4 sqrt 6)/3`
  3. `text(Proof)\ \ text{(See Worked Solutions)}`
  4. `(7 pi)/12`
Show Worked Solution

a.  `underset ~r (t) = (2 sqrt (t^2 + 2) – t^2) underset ~i + (2 sqrt (t^2 + 2) +2t) underset ~j`

  `underset ~v(t)` `=dot underset ~r(t)`
    `= (2(2t)(1/2)(t^2 + 2)^(-1/2) – 2t) underset ~i + (2(2t)(1/2)(t^2 + 2)^(-1/2) + 2)underset ~j`
    `= ((2t)/sqrt(t^2 + 2) – 2t) underset ~i + ((2t)/sqrt(t^2 + 2) + 2) underset ~j`

 

b.    `underset ~v(1)` `= (2/sqrt(1 + 2) – 2)underset ~i + (2/sqrt(1 + 2) + 2) underset ~j`
    `= (2/sqrt 3 – 2) underset ~i + (2/sqrt 3 + 2)underset ~j`
  `|\ underset ~v(1)\ |` `= sqrt((2/sqrt 3 – 2)^2 + (2/sqrt 3 + 2)^2)`
    `= sqrt(4/3 – 8/sqrt 3 + 4 + 4/3 + 8/sqrt 3 + 4)`
    `= sqrt(8/3 + 8)`
    `= sqrt(32/3)`
    `= (4sqrt2)/sqrt3`
    `= (4 sqrt 6)/3`

♦ Mean mark part (c) 41%.

c.    `(dy)/(dt)` `= (dy)/(dx) xx (dx)/(dt)`
  `(dy)/(dx)` `=((dy)/(dt))/((dx)/(dt))`
  `:. (dy)/(dx)|_(t=1)` `= (2/sqrt 3 + 2)/(2/sqrt 3 – 2)`
    `= ((2 + 2 sqrt 3)/sqrt 3) xx (sqrt 3/(2 – 2 sqrt 3))`
    `= (2 + 2 sqrt 3)/(2 – 2 sqrt 3)`
    `= (1 + sqrt 3)/(1 – sqrt 3)`

 

d.   `text(At)\ \ t=0:` 

♦♦ Mean mark part (d) 32%.

`underset ~r(0) = 2 sqrt 2 underset ~i + 2 sqrt 2 underset ~j`

`theta_1` `= tan^(-1)((2 sqrt 2)/(2 sqrt 2)) = pi/4`
`theta_2` `= tan^(-1)(1/sqrt 3)=pi/6`

 
`text(Let)\ \ theta=\ text(angle between the vectors:)`

`theta` `= pi – theta_1 – theta_2`
  `= pi – pi/4 – pi/6`
  `= (12 pi – 3 pi – 2 pi)/12`
  `= (7 pi)/12`

Filed Under: Position Vectors as a Function of Time Tagged With: Band 3, Band 4, Band 5, smc-1178-20-Find r(t) v(t) a(t), smc-1178-50-Other

Calculus, SPEC1 2012 VCAA 8

The velocity, `v` m/s, of a body when it is `x` metres from a fixed point `O` is given by

`v = (2x)/sqrt(1 + x^2).`

Find an expression for the acceleration of the body in terms of `x` in simplest form.  (3 marks)

Show Answers Only

`(4x)/(1 + x^2)^2`

Show Worked Solution
`v` `= (2x)/sqrt (1 + x^2)`  
`v^2` `=(4x^2)/(1+x^2)`  
`1/2 v^2` `= (2x^2)/(1 + x^2)`  

 

`a` `= d/(dx) (1/2 v^2)`
  `= d/(dx) ((2x^2)/(1 + x^2))`
  `= ((1 + x^2) (4x) – (2x^2) (2x))/(1 + x^2)^2`
  `= (4x)/(1 + x^2)^2`

Filed Under: Motion (SM) Tagged With: Band 4, smc-1159-20-Motion as f(x)

Calculus, SPEC1 2012 VCAA 7

Consider the curve with equation  `y = (x - 1) sqrt (2 - x),\ \ 1 <= x <= 2.`

Calculate the area of the region enclosed by the curve and the `x`-axis.  (3 marks)

Show Answers Only

`4/15`

Show Worked Solution

`x – 1 >= 0\ \ text(for)\ \ \ 1 <= x <= 2`

`sqrt(2 – x) >= 0\ \ text(for)\ \ \ 1 <= x <= 2`

`:. (x – 1) sqrt(2 – x) >=0\ \ text(for)\ \ \ 1 <= x <= 2`
 

`text(Let)\ \ u=2-x\ \ =>\ \ x=2-u`

`(du)/dx = -1\ \ =>\ \ dx = -du`

`text(When)\ \ x=2,\ \ u=0`

`text(When)\ \ x=1,\ \ u=1`
 

`A` `= int_1^2 (x – 1) sqrt(2 – x)\ dx`
  `= int_1^0 -(2 – u -1) u^(1/2)\ du`
  `= int_1^0 (u-1) u^(1/2)\ du`
  `= int_1^0 u^(3/2) – u^(1/2)\ du`
  `= [2/5u^(5/2)-2/3 u^(3/2)]_1^0`
  `= [0-(2/5-2/3)]`
  `= -((6-10))/15`
  `= 4/15`

Filed Under: Arc Lengths, Areas and Other Tagged With: Band 4, smc-1181-20-Area Under Curves

Calculus, SPEC1 2012 VCAA 6

Find the gradient of the tangent to the curve  `xy^2 + y + (log_e (x - 2))^2 = 14`  at the point  `(3, 2).`  (3 marks)

Show Answers Only

`(dy)/(dx) = -4/13`

Show Worked Solution

`xy^2 + y + (log_e (x – 2))^2 = 14`

`text(Using implicit differentiation:)`

`d/(dx) (xy^2) + d/(dx) (y) + d/(dx) ((ln (x – 2))^2) = d/(dx)(14)`

`d/(dx) (x) ⋅ y^2 + d/(dx) (y^2) ⋅ x + (dy)/(dx) + 2 xx 1/(x – 2) xx ln(x – 2) = 0`

`y^2 + 2xy* (dy)/(dx) + (dy)/(dx) + (2 ln (x – 2))/(x – 2) = 0`

`text{At (3,2):}`

`2^2 + 2(2)(3) m + m + (2 ln(1))/1` `= 0`
`4 + 12m + m` `= 0`
`13m` `= -4`
`:. m` `= -4/13`

Filed Under: Tangents and Curve Sketching Tagged With: Band 4, smc-1182-10-Find gradient, smc-1182-50-Implicit functions

Calculus, SPEC1 2012 VCAA 5

Let  `y = arctan (2x).`

Find the value of `a` given that  `(d^2y)/(dx^2) = ax ((dy)/(dx))^2`, where `a` is a real constant.  (3 marks)

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Show Answers Only

`a = -4`

Show Worked Solution
`(dy)/(dx)` `= 2x xx (1/(1 + (2x)^2))`
  `= 2/(1 + 4x^2)`
  `= 2(1 + 4x^2)^{-1}`
   
`(d^2y)/(dx^2)` `= 2(8x)(-1)(1 + 4x^2)^(-2)`
  `= (-16x)/(1 + 4x^2)^2`

 

`(d^2y)/(dx^2)` `= ax ((dy)/(dx))^2`
`(-16x)/(1 + 4x^2)^2` `= ax (2/(1 + 4x^2))^2`
  `= (4ax)/(1 + 4x^2)^2`

 

`4a` `= -16`
`:. a` `= -4`

Filed Under: Equations Tagged With: Band 4, smc-5161-10-1st/2nd deriv equations

Calculus, SPEC1 VCE SM-Bank 5

Find  `int(3x^2 + 8)/(x(x^2 +4))\ dx`.  (3 marks)

--- 7 WORK AREA LINES (style=lined) ---

Show Answers Only

` 2log_e x + 1/2log_e(x^2 + 4) + c` 

Show Worked Solution
`(3x^2 + 8)/(x(x^2 +4))` `=  a/x + (bx + c)/(x^2 + 4)`
`3x^2 +8` `=ax^2 + 4a+ bx^2 + cx`
  `=(a+b)x^2+cx+4a`
   

 `a + b = 3, \ c = 0, \ 4a = 8`

`:.a = 2, b = 1, c = 0`

`int(3x^2 + 8)/(x(x^2 +4))\ dx` `= int2/x\ dx + int x/(x^2 + 4)\ dx`
  `= 2log_e x + 1/2log_e(x^2 + 4) + c` 

Filed Under: Partial Fractions and Other Integration (SM) Tagged With: Band 4, smc-2565-20-Cubic denom, smc-2565-60-PF not given

Complex Numbers, SPEC1 2012 VCAA 3

Consider the equation  `z^3-z^2-2z-12 = 0, \ z in C.`

  1. Given that  `z = 2 text(cis) ((2pi)/3)`  is a root of the equation, find the other two roots in the form  `a + ib`, where  `a, b in R.`   (3 marks)

    --- 7 WORK AREA LINES (style=lined) ---

  2. Plot all of the roots clearly on the Argand diagram below.   (1 mark)

    --- 0 WORK AREA LINES (style=lined) ---

     

     


Show Answers Only
  1. `z_2 = -1-i sqrt 3`
    `z_3 = 3 + 0i`
     
  2.  

Show Worked Solution

a.   `text(Given)\ \  z = 2 text(cis)((2 pi)/3)\ \ text(is a root, and)`

`z^3-z^2-2z-12 = 0\ \ text(has real coefficients,)`

`=> z= 2 text(cis)(-(2 pi)/3)\ \ text{is a root (conjugate).}`

`=> text(Roots:)\ \ -1+sqrt3i,\ \ -1-sqrt3i`
 

`(z-alpha) (z-beta) (z-gamma) = z^3-z^2-2z-12`
 

`text(Using)\ \ alpha beta gamma = 12:`

`(-1 + i sqrt 3) (-1-i sqrt 3) gamma` `=12`  
`((-1)^2-(sqrt3i)^2)gamma` `=12`  
`4gamma` `=12`  
`gamma` `=3`  

 
`:.\ text(Other two roots:)`

♦♦ Mean mark part (b) 33%.

`z_2` `= -1-i sqrt 3`
`z_3` `= 3 + 0i`

 

b.   

Filed Under: Factors and Roots (SM) Tagged With: Band 4, Band 5, smc-1172-20-Cubic roots, smc-1172-60-Sketch solutions

Calculus, SPEC1 2012 VCAA 1

Find an antiderivative of  `(6 + x)/(x^2 + 4).`  (2 marks)

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`3 tan^-1(x/2) + 1/2 log_e (x^2 + 4)`

Show Worked Solution

`int (6 + x)/(x^2 + 4)\ dx`

`= int 6/(x^2 + 4)\ dx + int x/(x^2 + 4)\ dx`

`= 3 int 2/(x^2 + 2^2)\ dx + 1/2 int (2x)/(x^2 + 4)\ dx`

`= 3 tan^-1(x/2) + 1/2 log_e (x^2 + 4)\ \ \ (c=0)`

Filed Under: Partial Fractions and Other Integration (SM) Tagged With: Band 4, smc-2565-70-Other

Mechanics, SPEC2 2013 VCAA 20 MC

A 5 kg parcel is on the floor of a lift that is accelerating downwards at 3 m/s².

The reaction, in newtons, of the floor of the lift on the parcel is

A.  `−15 + 5g`

B.   `15 + 5g`

C.  `−15 + 3g`

D.  `−15 − 5g`

E.   `15 + 3g`

Show Answers Only

`A`

Show Worked Solution

`text(Let)\ R\ text(be the reaction force of the floor on the 5kg parcel.)`

`sum F` `= 5g – R`
`5xx3` `= 5g-R`
`:. R` `=-15 +5g`

 
`=> A`

Filed Under: Force, Momentum and Motion (SM) Tagged With: Band 4, smc-1174-50-Lifts

Calculus, SPEC2 2013 VCAA 19 MC

A tourist in a hot air balloon, which is rising at 2 m/s, accidentally drops a camera over the side and it falls 100 m to the ground.

Neglecting the effect of air resistance on the camera, the time taken for the camera to hit the ground, correct to the nearest tenth of a second, is

A.   4.3 s

B.   4.5 s

C.   4.7 s

D.   4.9 s

E.   5.0 s

Show Answers Only

`C`

Show Worked Solution

`u = 2, s = −100, a = -9.8`

`s` `= ut + 1/2at^2`
`-100` `= 2t – 4.9t^2`
`0` `= 4.9t^2 – 2t – 100`

 
`text(Solve:)\ \ 4.9t^2 – 2t – 100=0\ \ text(for)\ \ t`

`t~~4.7\ \ text(sec)`

`=> C`

Filed Under: Motion (SM) Tagged With: Band 4, smc-1159-10-Motion as f(t), smc-1159-50-Projectiles

Calculus, SPEC2 2013 VCAA 18 MC

A particle moves in a straight line such that its acceleration is given by  `a = sqrt(v^2 - 1)` , where `v` is its velocity and `x` is its displacement from a fixed point.

Given that  `v = sqrt2`  when  `x = 0`, the velocity `v` in terms of `x` is

A.   `v = sqrt(2 + x)`

B.   `v = 1 + |\ x + 1\ |`

C.   `v = sqrt(2 + x^2)`

D.   `v = sqrt(1 + (1 + x)^2)`

E.   `v = sqrt(1 + (x - 1)^2)`

Show Answers Only

`D`

Show Worked Solution
`v(dv)/(dx)` `= sqrt(v^2 – 1)`
`(dv)/(dx)` `= sqrt(v^2 – 1)/v`
`(dx)/(dv)` `= v/sqrt(v^2 – 1)`
`x` `=int v/sqrt(v^2 – 1)\ dv`
  `= sqrt(v^2 – 1) + c`

 
`text(When)\ \ x=0, \ v = sqrt2\ \ =>\ \ c = −1`

`x` `= sqrt(v^2 – 1) -1`
`v^2` `= 1 + (1 + x)^2`

 
`:. v = sqrt(1 + (1 + x)^2)`

`=> D`

Filed Under: Motion (SM) Tagged With: Band 4, smc-1159-30-a=f(v)

Vectors, SPEC2 2013 VCAA 17 MC

Consider the four vectors  `underset~a = underset~j + 3underset~k`,  `underset~b = underset~i - 4underset~k`,  `underset~c = 3underset~j - k`  and  `underset~d = 2underset~j + underset~k`.

Which one of the following is a linearly dependent set of vectors?

  1. `{underset~a, underset~b, underset~c}`
  2. `{underset~a, underset~c, underset~d}`
  3. `{underset~a, underset~b, underset~d}`
  4. `{underset~b, underset~c, underset~d}`
  5. `{underset~a, underset~b}`
Show Answers Only

`B`

Show Worked Solution

`underset ~b\ \ text(is the only vector which has an)\ \ i\ \ text(component.)`
 

`text(The other three vectors are on the same plane are therefore`

`text(linearly dependent.)`

`=> B`

Filed Under: Basic Concepts and Calculations Tagged With: Band 4, smc-1176-50-Linear dependence

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