Alternate angles in parallel lines are equal.
A pair of angles are said to be alternate if
In these images, the alternate angles are marked.
We can use a picture like this to help us remember this rule.
Alternate angles in parallel lines are equal.
(To help remember this is sometimes referred to as the z rule).
This interactive shows you how alternate angles are equal. You can move the parallel lines, and the transversal, by moving the blue points. This will create different angles, and you can view the angles one at a time or both together.
Calculate $x$x giving reasons for your answer.
Using only alternate angles, calculate $x$x