** is an isosceles country in which AB=AC. Side BA is produced to D such that AD=AB (see figure). Show that is a right angle.**

**Solution:**

AB=AC ** (Given)**

It means that **(In triangle, angles opposite to equal sides are equal) **

Let **(1)**

AC=AD **(Given)**

It means that **(In triangle, angles opposite to equal sides are equal) **

Let **(2)**

In , we have

**(Angle sum property of triangle)**

Putting **(1)** and **(2)** in the above equation, we get

Therefore,