# Alternate Interior Angles

When two lines are crossed by another line (called the Transversal):

**Alternate Interior Angles** are a **pair of angles** on the inner side of each of those two lines but on opposite sides of the transversal.

In this example c and f are a pair of Alternate Interior Angles

Also d and e are a pair of Alternate Interior Angles

To help you remember: the angle pairs are on **Alternate** sides of the Transversal, and they are on the **Interior** of the two crossed lines.

## Parallel Lines

When the two lines being crossed are Parallel Lines the **Alternate Interior Angles are equal**.

images/parallel-pair.js

*(Click on "Alternate Interior Angles" to have them highlighted for you.)*

2113,2114