Geometry and TrigonometryMediumOther angles of an isosceles triangle with an obtuse angle
Geometry and Trigonometry practice question
One angle of an isosceles triangle measures 100°. What is the measure, in degrees, of each of the other two angles?
Answer: 40
A triangle can't have two 100° angles (that would exceed 180°), so the 100° angle is the vertex angle and the other two are the equal base angles: (180 − 100)/2 = 40 each.
Common wrong answers
- If you answered 50
- 50 would be right if the given angle were 80°; here 180 − 100 = 80, halved is 40.
- If you answered 80
- 80 is 180 − 100, the two remaining angles TOGETHER; each is half of that.
- If you answered 100
- Two more 100° angles would give a total of 300°, which is impossible.
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