Angles in triangles for 11+ maths
21 October 2026
Angles in triangles
Understanding angles in triangles is essential for 11+ maths. Every triangle, no matter its shape, has angles that add up to 180 degrees.
Why 180 degrees matters
This rule is true for all triangles: equilateral, isosceles and scalene. If you know two angles, you can always find the third.
Worked example
A triangle has two angles: 50° and 60°.
First, add the two known angles: 50 + 60 = 110.
Next, subtract this sum from 180: 180 - 110 = 70.
The correct answer is 70. The third angle is 70°.
Key insight: If you forget the 180° rule, remember that the three angles in any triangle always make a straight line when placed together. This helps you check your work and avoid mistakes.
