Geometry and TrigonometryVery hardInterior angles from an exterior angle
Geometry and Trigonometry practice question
In triangle ABC, the exterior angle at vertex C measures 130°, and the measure of angle A is 20° greater than the measure of angle B. What is the measure, in degrees, of angle B?
Answer: 55
An exterior angle equals the sum of the two remote interior angles: A + B = 130. With A = B + 20, 2B + 20 = 130, so B = 55.
Common wrong answers
- If you answered 50
- 50 is angle C (180 − 130).
- If you answered 65
- 65 comes from halving 130 without allowing for the 20° difference.
- If you answered 75
- 75 is angle A.
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