## Pairs of angles

Two parallel lines crossed by another line (called transversal) form a special pairs of angles:

**Alternate interior angles** are formed on opposite sides of the transversal (green pair, blue pair). When the pair of lines are parallel, the resulting alternate interior angles are congruent (equal to each other). Each green and blue angle are
supplementary (green+blue=180°)

**Alternate exterior angles** are formed on opposite sides of the transversal on the outside (green pair, blue pair). When the pair of lines are parallel, the resulting alternate interior angles are congruent (equal to each other). Again, each green and blue angle are
supplementary (green+blue=180°)

**Corresponding angles** are the angles in matching corners (four pairs of different color). When the pair of lines are parallel, the corresponding angles are congruent (equal to each other).

**Consecutive interior angles** are formed on the same sides of the transversal between the lines (green pair, blue pair). When the pair of lines is parallel, the resulting consecutive interior angles are supplementary (blue+blue=180°, green+green=180°).

**Consecutive exterior angles** are formed on the same sides of the transversal outside the lines (green pair, blue pair). When the pair of lines is parallel, the resulting consecutive exterior angles are supplementary (blue+blue=180°, green+green=180°).