The measure of the vertex angle of an isosceles triangle is 120°. what is the measure of a base angle?

(1) Let x = the measure of each base angle.

(2) Set up an equation and solve for x.

base angle + base angle + 120 degrees = 180 degrees

x + x + 120 degrees = 180 degrees

2x + 120 = 180

2x = 180 - 120

2x = 60

x = 60/2

x = 30

Each base angle of triangle ABC measures 30 degrees.

its ok