Geometry and TrigonometryVery hardRemote interior angles from an exterior angle
Geometry and Trigonometry practice question
In triangle ABC, side BC is extended beyond C, forming an exterior angle of 115 degrees at C. The measure of angle A is 65 degrees. What is the measure, in degrees, of angle B?
Answer: 50
An exterior angle equals the sum of the two remote interior angles: 115 = 65 + B, so B = 50.
Common wrong answers
- If you answered 65
- 65 degrees is angle A; B makes up the rest of the exterior angle: 50.
- If you answered 115
- 115 degrees is the exterior angle itself; B is part of its split with A.
- If you answered 130
- Do not double the 65; the exterior angle 115 splits as A + B, so B = 115 − 65 = 50.
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