Geometry · JSS 2
Angles in a triangle
Find a missing angle in any triangle.
- A + B + C = 180°
What the letters mean
- A, B, C
- the three angles inside the triangle
Worked example
Two angles of a triangle are 65° and 48°. Find the third.
Step 1: Subtract from 180°
180° − 65° − 48° = 67°
Final answer: 67°
An exterior angle equals the sum of the two opposite interior angles.
See it
Play with this picture from the Angles in a Triangle lesson.
60° + 48° + 72° = 180°
This is an acute-angled, scalene triangle. Drag any corner!
Put the three angles together and they make a straight line: 180°.