Geometry and TrigonometryVery hardAngle formed by an angle bisector
Geometry and Trigonometry practice question
In triangle ABC, the measure of angle B is 50° and the measure of angle C is 70°. The bisector of angle A meets side BC at point D. What is the measure, in degrees, of angle ADB?
Answer: 100
Angle A = 180 − 50 − 70 = 60, so angle BAD = 30. In triangle ABD, angle ADB = 180 − 30 − 50 = 100.
Common wrong answers
- If you answered 60
- 60 is angle A itself.
- If you answered 80
- 80 is angle ADC, the other angle at D.
- If you answered 130
- 130 is 180 − 50, forgetting the half-angle at A.
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