CBSE Class 10 Maths (Standard) 2020 · Paper 30/3/1 · Question 37(a)

Triangles 4 marks Medium

In an equilateral triangle

A B C

D

is a point on the side

B C

such that

B D = \frac{1}{3} B C

. Prove that

9 A D^{2} = 7 A B^{2}

Answer

Since

A D^{2} = \frac{7}{9} a^{2}

and

A B = a

, we get

9 A D^{2} = 7 a^{2} = 7 A B^{2}

. Hence proved.

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