Geometry and TrigonometryMediumTriangle angle from an exterior angle
Geometry and Trigonometry practice question
In triangle PQR, the exterior angle at P measures 110° and angle Q measures 45°. What is the measure, in degrees, of angle R?
Answer: 65
The exterior angle at P equals the sum of the two remote interior angles: 110 = 45 + R, so R = 65.
Common wrong answers
- If you answered 25
- 25 is 70 − 45, using the interior angle at P instead of the exterior.
- If you answered 70
- 70 is the interior angle at P (180 − 110), not angle R.
- If you answered 135
- 135 is 180 − 45, forgetting angle P altogether.
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