Question

Vertex angle ( A ) of isosceles triangle ( ABC ) measures 70°. What is the measure, in degrees, of an exterior angle at ( B )?

a) 140°
b) 70°
c) 35°
d) 110°

Answer 1

The measure of the exterior angle at vertex B in an isosceles triangle is 125°.

Step-by-step explanation:

The measure of an exterior angle at vertex B in an isosceles triangle is equal to the sum of the measures of the two non-adjacent interior angles. In this case, the vertex angle A measures 70°, so the other two interior angles measure (180° - 70°)/2 = 55° each. Therefore, the measure of the exterior angle at B is 55° + 70° = 125°.