Angles in a triangle add up to 180° and in quadrilaterals add up to 360°. Angles can be calculated inside semicircles and circles. Parallel lines in shapes can form corresponding and alternate angles.

Parallel lines are straight lines which have the same direction and so never meet. Parallel lines are marked with an arrow as shown below.

In diagrams, parallel lines can form:

These are sometimes known as 'F' angles.

The diagram below shows parallel lines being intersected by another line.

The two angles marked in this diagram are called corresponding angles and are equal to each other.

The two angles marked in each diagram below are called alternate angles or Z angles. They are equal.

Vertically opposite angles are so called because they are opposite each other at a vertex.

The two angles marked in each of these diagrams are called vertically opposite angles and are equal.