Find angle x in the given figure.

We know that in an isosceles triangle, the angles opposite the equal sides are equal.

Since ΔABC is an isosceles with AB = AC.

∴ ∠B = ∠C = x

By the angle sum property, we have

∠A + ∠B + ∠C = 180^o

⇒ 100^o + x + x = 180^o

⇒ 2x = 180^o − 100^o

⇒ 2x = 80^o

⇒ x = 40^o