Question

The measure of the vertex angle of an isosceles triangle is 120. What is the measure of the base angle?

Answer 1

We know that the sum of interior angles in the triangle is 180°.
2 α + β = 180°
The vertex angle is β = 120°
2 α + 120° = 180°
2 α = 180° - 120°
2 α = 60°
α = 60° : 2 = 30°
Answer:
The base angle is : α = 30°