### Have you noticed that when a transversal cuts two parallel lines; all the acute angles are congruent among them, and all the obtuse angles are congruent among them, and that if you add one acute and one obtuse they are supplementary? Can you identify consecutive interior angles? Or Alternate interior angles? What about corresponding angles?

### By working in this lesson, you will clarify your understanding about these angle pairs. The lesson starts by introducing angle pairs using animations and colors; and then it jumps to explain what happens if the lines are parallel. In a very clear way it tells you what angle pairs are congruent, and which ones are supplementary. You will be able to assess your acquired knowledge after most of the examples, by answering a similar problem.

** Lesson's Content **

** Lesson's Glossary **

**Alternate exterior angles **

Exterior angles on alternate sides of the transversal (not on the same parallel line)

** Alternate interior angles **

Interior angles on alternate sides of the transversal (not on the same parallel line)

** Complementary angles **

Two positive angles that when added give 90 degrees.

**Corresponding angles **

Any pair of angles in similar locations with respect to a transversal

**Parallel lines **

Two lines in the same plane that never cross or intersect.

**Perpendicular lines **

Two segments, rays, or lines that form a 90 degree angle.

**Supplementary angles **

Two angles whose measures, when added together, equal 180 degrees.

**Transversal **

A line that intersects others.

**Vertical angles **

Two angles that share a common vertex and whose sides form two straight lines.

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