Question

In an isosceles triangle, if the vertex angle is twice the sum of the base angles, then the measure of vertex angle of the triangle is

A. 100°

B. 120°

C. 110°

D. 130°

Answer 1

Let the base angles be x each,

Vertex angle = 2(x + x) = 4x

Now, since the sum of all the angles of a triangle is 180°

x + x + 4x = 180°

6x = 180°

x = 30°

Therefore, vertex angle= 4x = 120°