Angles

An angle measures a turn. A full turn is 360°, a half turn 180° and a quarter turn (a right angle) 90°. Angles get their names from their size.

Key facts

  • Acute: less than 90°.
  • Right angle: exactly 90° (shown with a little square).
  • Obtuse: between 90° and 180°.
  • Reflex: more than 180°.
  • Measure with a protractor: put the centre on the corner and the zero line on one arm.

Worked examples

Example 1

What type of angle is 135°, and roughly how does it look?

  1. It is more than a right angle (90°).
  2. It is less than a straight line (180°).
  3. So it is obtuse: a right angle and half of another one. 90 + 45 = 135

Answer: Obtuse

Example 2

A reflex angle and the angle next to it make a full turn. The small angle is 70°. Find the reflex angle.

  1. Angles round a point add to 360°. 360 − 70 = 290
  2. So the reflex angle is 290°

Answer: 290°