Angles in a triangle add to 180°
The three interior angles of any triangle sum to 180°.
The common mistake
Using 360° (the total for a quadrilateral) or forgetting an isosceles pair is equal.
Instead: Add the known angles and subtract from 180°. In an isosceles triangle, the two base angles match.
Worked example with Guide me
Two angles are 48° and 71°. Find the third.
- Sugar · Add the two you know.Student · 119°.
- Sugar · Subtract from 180°.Student · 61°.
Answer: 61°
Try 3 practice questions
1. Angles 90° and 35° — third?
Show answer
55°
2. Isosceles with top angle 40° — each base angle?
Show answer
70°
3. All three equal — each angle?
Show answer
60°
Quick answers
- What is the most common mistake with angles in a triangle add to 180°?
- Using 360° (the total for a quadrilateral) or forgetting an isosceles pair is equal.
- How do I get angles in a triangle add to 180° right?
- Add the known angles and subtract from 180°. In an isosceles triangle, the two base angles match.
- Can you show a worked example?
- Two angles are 48° and 71°. Find the third. 61°
Related concepts
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