Straight line angles
If one angle is 130°, the angle next to it on a straight line is 50°.
Angles on a straight line add to 180 degrees.
Year 6
Recognise angles where they meet at a point, are on a straight line, or are vertically opposite, and find missing angles
Use angle facts at a point, on a straight line and in vertically opposite pairs to find unknown angles.
Lesson overview
Geometry - properties of shape
Angles around a point total 360 degrees. Angles on a straight line total 180 degrees. Vertically opposite angles are equal.
Vertically opposite angles
Opposite angles made by crossing lines are equal.
This fact helps fill missing values quickly.
Worked example
Two angles on a straight line are 122° and ? Find the missing angle.
| Known | Total |
|---|---|
| 122° | 180° |
- Angles on a straight line total 180°.
- Subtract the known angle from 180°.
- 180° - 122° = 58°.
- So the missing angle is 58°.
Try it
Decide whether the angles are on a line, around a point or vertically opposite first.
Question 1
Angles on a straight line total:
Question 2
Angles around a point total:
Question 3
If one angle on a straight line is 130°, the other is:
Question 4
Vertically opposite angles are:
Question 5
If angles around a point include 90°, 120° and 80°, the missing angle is:
Common mistakes
Watch for these when working through the lesson.
- Using 360° when the angles are only on a straight line.
- Forgetting that vertically opposite angles are equal.
- Subtracting from the wrong total.
Related topics
These ideas fit closely with this lesson.
- Compare and classify geometric shapes.
- Draw 2-D shapes using given dimensions and angles.