There are certain special angles that we should know about. The teacher will draw each of these in the board so we can consider them.

A right-angle takes up 90º, so if it is broken up into various angles, those angles must sum to 90º. We call angles that sum to 90º complementary angles.

A straight-angle contains 180º, so if it is broken up into various angles, those angles must sum to 180º. We call angles that sum to 180º supplementary angles.

Angles around a point sum to 360º.

Vertically opposite angles are equal.

Worked Example

Without using a protractor, calculate the size of the missing angles:

Exercise

Answers