Question

the vertex angle of an isosceles triangle measures 40°. what is the measure of a base angle? 40° 70° 100°

Explanation:

Step1: Sum of angles in triangle

Sum = 180°, vertex angle = 40°

Step2: Let base angle be x

2x + 40° = 180°

Step3: Solve for x

2x = 140° ⇒ x = 70°

Answer:

B. 70°