The two triangles below are similar.
Find the length of \(ED\). (3 marks)
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The two triangles below are similar.
Find the length of \(ED\). (3 marks)
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\(ED = 15\)
\(\text{Using Pythagoras in}\ \Delta ABC: \)
\( AB=\sqrt{13^2-12^2}=\sqrt{25}=5 \)
\(\text{Scale factor}\ = \dfrac{FD}{AC} = \dfrac{39}{13} = 3 \)
\(\therefore ED = 3 \times AB = 3 \times 5 = 15 \)
Prove that the two triangles in the right cone pictured below are similar. (2 marks)
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\(\text{Proof (See Worked Solution)}\)
\(\angle ACD \ \text{is common to}\ \Delta ACE\ \text{and}\ \Delta BCD \)
\(\angle CAE=\angle CBD=90^\circ \ \text{(Right cone)} \)
\(\therefore \Delta ACE\ \text{|||}\ \Delta BCD\ \ \text{(equiangular)}\)
Show that \(\Delta ACD\) and \(\Delta DCB\) in the figure below are similar. (2 marks)
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\(\text{Proof (See Worked Solution)}\)
\(\angle BDC = 180-(88+44) = 48^{\circ} \ \text{(angle sum of Δ)} \)
\(\angle CAD = \angle CDB = 48^{\circ} \)
\(\angle ACD=44^{\circ} \ \text{is common to}\ \Delta ACD\ \text{and}\ \Delta BCD \)
\(\therefore \Delta ACD\ \text{|||}\ \Delta DCB\ \ \text{(equiangular)}\)
\(\text{Proof (See Worked Solution)}\)
\(\angle PQT = \angle SQR \ \text{(vertically opposite)} \)
\(\dfrac{PQ}{QS} = \dfrac{2.5}{5} = \dfrac{1}{2} \)
\(\dfrac{TQ}{QR} = \dfrac{2}{4} = \dfrac{1}{2} \)
\(\therefore \Delta PQT\ \text{|||}\ \Delta SQR\ \ \text{(sides adjacent to equal angles in proportion)}\)
Prove that this pair of triangles are similar. (2 marks)
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\(\text{Proof (See Worked Solution)}\)
\(\angle ACD = \angle BEA \ \text{(given)} \)
\(\angle BAE\ \text{is common to}\ \Delta ACD\ \text{and}\ \Delta BEA \)
\(\therefore \Delta ACD\ \text{|||}\ \Delta BEA\ \ \text{(equiangular)}\)
Prove that this pair of triangles are similar. (3 marks)
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\(\text{Proof (See Worked Solution)}\)
\(\text{Find unknown side}\ (x)\ \text{of smaller triangle}\)
\(\text{Using Pythagoras:}\)
\(x=\sqrt{5^2-4^2} = \sqrt{9} = 3\)
\(\dfrac{AC}{DE} = \dfrac{5}{15} = \dfrac{1}{3} \)
\(\dfrac{BC}{EF} = \dfrac{3}{9} = \dfrac{1}{3} \)
\(\angle ABC = \angle DEF = 90^{\circ} \ \ \text{(given)} \)
\(\therefore \Delta ABC\ \text{|||}\ \Delta DEF\ \ \text{(hypotenuse and second side of right-angled triangle in proportion)}\)
Prove that this pair of triangles are similar. (2 marks)
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\(\text{Proof (See Worked Solution)}\)
\(\dfrac{AB}{GH} = \dfrac{11}{22} = \dfrac{1}{2} \)
\(\dfrac{BC}{FG} = \dfrac{3.5}{7} = \dfrac{1}{2} \)
\(\angle ABC = \angle FGH = 95^{\circ} \ \ \text{(given)} \)
\(\therefore \Delta ABC\ \text{|||}\ \Delta HGF\ \ \text{(sides adjacent to equal angles in proportion)}\)
Prove that this pair of triangles are similar. (2 marks)
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\(\text{Proof (See Worked Solution)}\)
\(\angle ABE = \angle CBD\ \ \text{(vertically opposite)} \)
\(\angle AEB = \angle BCD\ \ \text{(alternate,}\ AE \parallel CD \text{)} \)
\(\therefore \Delta ABE\ \text{|||}\ \Delta DBC\ \ \text{(equiangular)}\)
Prove that this pair of triangles are similar. (2 marks)
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\(\text{Proof (See Worked Solution)}\)
\(\dfrac{RP}{AC} = \dfrac{18}{12} = \dfrac{3}{2} \)
\(\dfrac{QR}{BA} = \dfrac{12}{8} = \dfrac{3}{2} \)
\(\dfrac{PQ}{CB} = \dfrac{9}{6} = \dfrac{3}{2} \)
\(\therefore \Delta PQR\ \text{|||}\ \Delta CBA\ \ \text{(three pairs of sides in proportion)}\)