Geometry and TrigonometryEasyThird angle of an isosceles triangle from its base angles
Geometry and Trigonometry practice question
An isosceles triangle has two angles that each measure 70°. What is the measure, in degrees, of the third angle?
Answer: 40
The angles of a triangle add to 180: 180 − 70 − 70 = 40.
Common wrong answers
- If you answered 20
- 20 is 40/2, halving for no reason.
- If you answered 70
- The third angle isn't required to equal the others; 70 + 70 + 70 would exceed 180.
- If you answered 110
- 110 is 180 − 70, subtracting only one of the two 70° angles.
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