Here is a definition:

Two lines are parallel if they are coplanar and do not intersect.

Now that we have established what it means to measure the relative arc lengths of angles, we will examine properties of both parallel lines and angles.

In the diagram above, lines AB and CD are parallel. What are some attributes of lines AB and CD?

Now look at this picture:

Here are some naming conventions we will use when talking about parallel lines:

Line EF is called a transversal.

Corresponding angles are angles that share the same locations relative to each other.

Angles on opposite sides of the transversal are called alternate angles.

Angles on the same side of the transversal are called same-side angles.

Angles ‘within’ the boundaries of the parallel lines are called interior angles.

Using the diagram on the first page, find the following:

All the corresponding angles:

_____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____

Now all the alternate interior angles:

_____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____

Now all the same side interior angles:

_____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____ _____