The quantity \(y\) varies inversely with the square of \(x\).
When \(x = 4, \ y = 10\).
Find the value of \(y\) when \(x = 8\). (2 marks)
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The quantity \(y\) varies inversely with the square of \(x\).
When \(x = 4, \ y = 10\).
Find the value of \(y\) when \(x = 8\). (2 marks)
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\(y=\dfrac{5}{2}\)
\(y \propto \dfrac{1}{x^2}\ \ \Rightarrow\ \ y= \dfrac{k}{x^2}\)
\(\text{When}\ \ x=4, \ y=10:\)
\(10= \dfrac{k}{4^2}\ \ \Rightarrow\ \ k=160\)
\(\text{Find}\ y\ \text{when}\ x=8:\)
\(y=\dfrac{160}{8^2}=\dfrac{5}{2}\)
A student believes that the time it takes for an ice cube to melt (`M` minutes) varies inversely with the room temperature `(T^@ text{C})`. The student observes that at a room temperature of `15^@text{C}` it takes 12 minutes for an ice cube to melt.
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\begin{array} {|c|c|c|c|}
\hline \ \ T\ \ & \ \ 5\ \ & \ 15\ & \ 30\ \\
\hline M & & & \\
\hline \end{array}
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a. `M=180/T`
b.
\begin{array} {|c|c|c|c|}
\hline \ \ T\ \ & \ \ 5\ \ & \ 15\ & \ 30\ \\
\hline M & 36 & 12 & 6 \\
\hline \end{array}
| a. | `M` | `prop 1/T` |
| `M` | `=k/T` | |
| `12` | `=k/15` | |
| `k` | `=15 xx 12` | |
| `=180` |
`:.M=180/T`
b.
\begin{array} {|c|c|c|c|}
\hline \ \ T\ \ & \ \ 5\ \ & \ 15\ & \ 30\ \\
\hline M & 36 & 12 & 6 \\
\hline \end{array}
The current of an electrical circuit, measured in amps `(A)`, varies inversely with its resistance, measured in ohms `(R)`.
When the resistance of a circuit is 28 ohms, the current is 3 amps.
What is the current when the resistance is 8 ohms? (2 marks)
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`10.5`
`A \prop 1/R\ \ =>\ \ A=k/R`
`text(When)\ \ A=3, \ R=28:`
| `3` | `=k/28` | |
| `k` | `=84` |
`text(Find)\ A\ \text{when}\ R=8:`
`A=84/8=10.5`