Question

Triangle ABC is shown. The measure of the interior angle at point A is
40
°
and the exterior angle at point C is
102
°
.

The exterior angle at B of the triangle A-B-C is x degrees.

What is the measure of angle x?

A.
62
°

B.
78
°

C.
102
°

D.
118
°

Answer 1

The exterior angle at C equals the sum of the opposite interior angles: 102 = A + B = 40 + B, so B = 62°. Then C = 180 − 40 − 62 = 78°. The exterior angle at B equals A + C = 40 + 78 = 118°.

Answer: D (118°).