160 Part 3: The Shape of the World
DEFINITION
Lines, rays or segments that meet to form a right angle are perpendicular.
Parallel lines are lines on the same plane that never intersect.Parallel lines all by themselves are not all that interesting. They just keep on going, never meet,
and don’t do anything exciting. When other lines get mixed up with parallel lines, however, some
more interesting things do happen.The Defining Angles
When parallel lines are cut by another line, called a transversal, eight angles are formed. Different
pairs from this group of eight are classified in different ways.As the transversal crosses the first line, it creates a cluster of four angles, labeled 1, 2, 3, and
4 in this picture. As it crosses the second line, it creates another cluster of four angles, labeled
5, 6, 7, a nd 8. In each cluster, there is an angle in the upper left position (1 from the top
cluster or 5 from the bottom). There are also angles in the upper right, lower left, and lower
right positions. The angle from the upper cluster and the angle from the lower cluster that are in
the same position are called corresponding angles.DEFINITION
A transversal is a line that intersects two or more other lines.
Corresponding angles are a pair of angles created when a transversal intersects two
parallel lines that are on the same side of the transversal and are both above or both
below the parallel lines.When parallel lines are cut by a transversal, corresponding angles are congruent. They have the
same measurements. 1 # 5, 2 # 6, 3 # 7, a nd 4 # 8.12
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