Angles that make a straight line add up to 180°. If one angle is 110°, the other is 180° − 110° = 70°. Angles around a point make a full turn, so they add up to 360°.
The three angles inside any triangle also add up to 180°. If two angles are 50° and 60°, the third is 180° − 50° − 60° = 70°. Add the angles you know, then subtract from the total.
Worked example
Angles of 35°, 79° and x lie on a straight line. Find x.
- Angles on a straight line add to 180°.
- 35 + 79 = 114, and 180 − 114 = 66.
Answer:x = 66°
Key words
- angles on a line
- add up to 180°
- angles at a point
- add up to 360°
- angles in a triangle
- add up to 180°
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Common Core-referenced: 4.MD.C.7