Finding Missing Angles in Triangles
Maths: Year 5 & 6 National Curriculum, topic 8.4.3
Missing Angles in a Triangle
To find a missing angle in a triangle, you need to remember that all the angles add up to 180°.
,w_800.png)
Equilateral triangle
- Equilateral triangles have 3 angles.
- All angles in an equilateral triangle are 60°.
,w_800.png)
Finding the missing angle
- You need to remember that the angles in a triangle add up to 180°.
- You also need to remember that the right angle is 90°.
,w_800.png)
Finding the missing angle 2
- Add the two known angles together.
- 40° + 90° = 130°
,w_800.png)
Finding the missing angle 3
- You know that all the angles in a triangle add up to 180°.
- You need to work out the difference between 180° and 130°.
- 180° − 130° = 50°
,w_800.png)
Finding the missing angle 4
- The missing angle is 50°.
Missing Angles in a Quadrilateral
To find a missing angle in a quadrilateral, you need to remember that all the angles add up to 360°. A quadrilateral is a four-sided shape (e.g. square, rectangle, parallelogram).
,w_800.png)
Missing angles in quadrilaterals
- Finding missing angles in a quadrilateral is very similar to triangles.
- But you need to remember that the angles in a quadrilateral add up to 360°.
- E.g. a square has four right angles (90°).
,w_800.png)
Finding the missing angle
- You need to remember that the angles in a quadrilateral add up to 360°.
,w_800.png)
Finding the missing angle 2
- Add the three known angles together.
- 96° + 102° + 80° = 278°
,w_800.png)
Finding the missing angle 3
- You know that all the angles in a quadrilateral add up to 360°.
- You need to work out the difference between 360° and 278°.
- 360° − 278° = 82°
,w_800.png)
Finding the missing angle 4
- The missing angle is 82°.
Test yourself on Finding Missing Angles in Triangles
What do the angles in a triangle add up to?
What is the missing angle in this triangle?
What is the missing angle in this triangle?
What is the missing angle in this triangle?
What is the missing angle in this triangle?