GEOMETRY

Angles On A Line

Learn the reliable method for angles on a line, then apply it to 11+ exam-style questions.

1 · WHAT YOU NEED TO KNOW

The idea

Angles On A Line questions require you to use properties and labels, not the apparent size of a drawing.

Picture itTrack the angle turn
Colourful playground markings showing shapes, equal sections, parallel lines and boundaries
2 · THE METHOD

Follow these steps

  1. Mark the information given on the diagram.
  2. Choose the relevant property or formula.
  3. Calculate one step at a time and include units.
3 · WORKED EXAMPLES

See the method in action

Example 1

Two angles lie on a straight line. One is 115°. What is the other angle?

Not drawn to scale115°?
  1. Angles on a straight line total 180°, so 180° − 115° = 65°.
Answer: 65°
Example 2

Two adjacent angles form a straight line. The larger angle is 38° greater than the smaller angle. What is the smaller angle?

Not drawn to scalexx + 38°
  1. Remove the 38° difference from 180°: 142°.
  2. Split the remainder equally: 142° ÷ 2 = 71°.
Answer: 71°
4 · ELEVENSPRINT TIP

A useful shortcut

Never rely on a diagram being drawn to scale unless the question says it is.

5 · COMMON MISTAKES

Watch out for these

Using a remembered number without checking the shape

Name the shape or angle rule before substituting values.

6 · TRY IT YOURSELF

Three fresh questions

Ready to check the method? You will get three fresh, validated questions.