Geometry and TrigonometryMediumThird exterior angle of a triangle
Geometry and Trigonometry practice question
The exterior angles of a triangle, one at each vertex, add up to 360°. Two of a triangle's exterior angles measure 110° and 130°. What is the measure, in degrees, of the third exterior angle?
Answer: 120
360 − 110 − 130 = 120.
Common wrong answers
- If you answered 60
- 60 is the interior angle at the third vertex (180 − 120), not its exterior angle.
- If you answered 240
- 240 is the sum of the two given angles, not the third.
- If you answered -60
- −60 is 180 − 240, using a triangle's INTERIOR total of 180; exterior angles total 360.
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