Warm Up
This lesson focuses on angle relationships formed when a transversal crosses a pair of parallel lines.Parallel lines are lines in a plane that will never intersect. Two parallel lines will be the same distance apart for their entire length. Lines A and B can be represented as parallel by 
. A parallelogram is a quadrilateral made from two pairs of parallel line segments.
Perpendicular lines are lines that meet at a right angle. Lines A and B can be represented as perpendicular by 
.
A transversal is a line that passes through two other lines at different points. A transversal will often cross parallel lines in this lesson.
If two or more angles form a straight line, the sum of their measures is 180°. Two angle measures that sum to 180° are called supplementary angles and two angle measures that sum to 90° are called complementary angles.
The Angle Relationships applet will allow you to explore some of the ideas you will learn about in this lesson. Use the applet to help you complete the following table.
Use the blue dots to adjust the diagram. Change the check-boxes to see different angle relationships.
| Angle Relationship | Description of the relationship | Sketch of the relationship | Describe any apparent relationship in the size of the angles |
|---|---|---|---|
| Opposite Angles | Angles opposite each other formed when two lines cross. |  |
Opposite angles always appear to be the same size. |
| Corresponding Angles | Angles on the same side of the transversal and on the same side of each parallel line. | ||
| Interior Angles | |||
| Exterior Angles | |||
| Alternate Interior | |||
| Alternate Exterior |