The vertical angle of an isosceles triangle is 100°. Find its base angles.

Consider an isosceles triangle ABC,

Such that:

AB = AC

Given,

Vertical ∠A is 100^o

To find: Base angle

Since, is isosceles,

∠B = ∠C (Angle equal to opposite sides)

And,

∠A + ∠B + ∠C = 180^o (Angles of triangle)

100^o + ∠B + ∠B = 180^o

∠B = 40^o

∠B = ∠C = 40^o