A **transversal** is any line that intersects two or more lines in the same plane but at different points. In Figure , line *t* is a transversal.

**Figure 1 **A transversal intersecting two lines in the same plane.

A transversal that intersects two lines forms eight angles; certain pairs of these angles are given special names. They are as follows:

**Corresponding angles** are the angles that appear to be in the same relative position in each group of four angles. In Figure , ∠l and ∠5 are corresponding angles. Other pairs of corresponding angles in Figure are: ∠4 and ∠8, ∠2 and ∠6, and ∠3 and ∠7.

**Figure 2 **A transversal intersecting two lines and forming various pairs of corresponding angles
alternate interior angles, alternate exterior angles, consecutive interior angles, and consecutive

exterior angles.

**Alternate interior angles** are angles within the lines being intersected, on opposite sides of the transversal, and are not adjacent. In Figure 2, ∠4 and ∠6 are alternate interior angles. Also, ∠3 and ∠5 are alternate interior angles.

**Alternate exterior angles** are angles outside the lines being intersected, on opposite sides of the transversal, and are not adjacent. In Figure 2, ∠l and ∠7 are alternate exterior angles. Also, ∠2 and ∠8 are alternate exterior angles.

**Consecutive interior angles** (same‐side interior angles) are interior angles on the same side of the transversal. In Figure 2, ∠4 and ∠5 are consecutive interior angles. Also, ∠3 and ∠6 are consecutive interior angles.

**Consecutive exterior angles** (same‐side exterior angles) are exterior angles on the same side of the transversal. In Figure 2, ∠l and ∠8 are consecutive exterior angles. Also, ∠2 and ∠7 are consecutive exterior angles.