Question

prove that in an isosceles triangle the exterior angle corresponding to the third angle is double each of the equal angles.​

Answer 1

A

/\

/ \

/ \

/_____ \

B C

Let equal ∠s= x° each.

Let y=3rd angle.

Given—> 3rd Angle=2(x°)

⇒180-y=2x

Proof—> Let's substitute x=50

Then, 180°-A=B+C

180-A=100

180-[180-{A+B}]=100 {I know that A =180 - sum of B and C}

180-[180-100]=100

180-80=100

100=100

180-A=B+C

This is proof by substitution.