Question

if the equal sides of an isosceles triangle are produced ,prove the exterior angles so formed are obtuse and equal

Answer 1

In a isosceles triangle the angles opposite to equal.
Therefore angle ABC=ACB
ABC+CBD=180°
ACB+BCE=180°
CBD=180°- ABC
BCE=180° - ACB
CBD=BCE (ABC=ACB therefore subtracting from 180 the difference is same)

In a triangle there cannot be 2 angles having measuring 90° or more.

So the angles are acute and since the angles are acute their linear pairs are obtuse