There are in a **complete** turn.

There are in **half** a turn (a straight line).

- Question
Find the size of angle :

There are in a complete turn, so

- Question
What is the size of angle ?

The angles on a straight line add up to , so .

The angles in a **triangle** add up to .

The angles in a **quadrilateral** add up to .

This works for any quadrilateral.