Angles and symmetry
Lesson 6 of 10
Angle rules
Objective. Use angles on a line, around a point and in a triangle.
The key idea
Angles on a straight line total 180°, angles around a point total 360°, and the angles of any triangle total 180°.
Worked example
A triangle has angles 65° and 40°. Find the third.
- 1Angles total 180°.
- 265 + 40 = 105.
- 3180 − 105 = 75.
Answer: 75°
Practice
Each question comes with a picture and a listen button. Try it first, then reveal the answer.
Common mistake. Using 360° for a triangle because a quadrilateral does.
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