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Mathematics

A triangle with sides 6, 9 and 12 units has area A sq. units. What is the area (in sq. units) of a triangle with sides 8, 12 and 16 units in terms of A?

  1. 32\dfrac{3}{2} A

  2. 43\dfrac{4}{3} A

  3. 169\dfrac{16}{9} A

  4. 2516\dfrac{25}{16} A

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Answer

We compare the ratios of the corresponding sides of the first triangle with sides 6, 9, 12 and the second triangle with sides 8, 12, 16.

k = 68=912=1216=34\dfrac{6}{8} = \dfrac{9}{12} = \dfrac{12}{16} = \dfrac{3}{4}.

Therefore, the two triangles are similar with scale factor of k = 34\dfrac{3}{4}. The ratio of Areas of two triangle is equal to square of it's scale factor.

Area1Area2=k2AArea2=(34)2AArea2=916Area2=169A.\Rightarrow \dfrac{\text{Area}1}{\text{Area}2} = k^2 \\[1em] \Rightarrow \dfrac{A}{\text{Area}2} = \Big(\dfrac{3}{4}\Big)^2 \\[1em] \Rightarrow \dfrac{A}{\text{Area}2} = \dfrac{9}{16} \\[1em] \Rightarrow \text{Area}_2 = \dfrac{16}{9}A.

Hence, option 3 is the correct option.

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