Triangle angle facts: step-by-step example
27 October 2026
Understanding triangle angle facts is a key part of 11+ Maths. Children often see questions where they need to find a missing angle in a triangle. Knowing the rule about the sum of angles helps them solve these quickly and with confidence.
Worked example
Find the missing angle in a triangle where two angles are 50° and 60°.
Step 1: Angles in a triangle add up to 180°.
Step 2: Add the two known angles.
50° + 60° = 110°
Step 3: Subtract this from 180°.
180° - 110° = 70°
Key insight: All three angles in a triangle always add up to 180°.
The missing angle is 70°.
After working through this example, your child will recognise how to use the triangle angle rule to find a missing value. They can now spot similar questions and practise using the same method. More practice questions like this are ready for them to try next.
