Two of the angles of a triangle have measures of 50° and 60°. Which number cannot be the measure of an exterior angle of this triangle?
A) 100°
B) 110°
C) 120°
D) 130°

Question

Quizplus · Accepted Answer

The measure of an exterior angle of a triangle is equal to the sum of the measures of the two interior angles that are not adjacent to it. In this case, the third interior angle measure would be 180° - 50° - 60° = 70°. Therefore, the measures of the possible exterior angles are 110° (60° + 50°), 120° (60° + 70°), and 130° (50° + 80°). However, an exterior angle cannot be greater than 180°, so 100° is not a possible measure for an exterior angle of this triangle.

Two of the Angles of a Triangle Have Measures of 50°