1.3 Parallel and Perpendicular Lines
Lines and Angles
Pacing:This lesson should take one to one and one-half class periods
Goal: Students will be introduced to parallel, perpendicular, and skew lines in this lesson. Transversals and the
angles formed by such are also introduced.
While example 1 shows students that it is possible for streets to be perpendicular or parallel, challenge students to
find roads that begin as parallel then intersect (or begin perpendicular and then become parallel).
Visualization! Show a map that has zoned roads in the fashion of example 1, perhaps in rural Ohio or Kansas.
Encourage students to compare this map with one of Atlanta, New York City, or Chicago.
Physical Model!Give each student a cube; it could be a die, box, etc. When discussing the definition of skew lines,
have students point to the lines you are referencing. This provides students a physical model in addition to allowing
you to do a quick assessment.
In Class Activity!Have students trace the top and bottom of a ruler to create pair of parallel lines. Then construct
an oblique line crossing through both parallel lines. Instruct students to number all 8 angles and color code each of
the terms found on page 131. Ask students to summarize each definition and how it relates to another angle in the
diagram.
Vocabulary!There are five ways to determine parallel lines: showing congruent corresponding angles or congruent
alternate interior angles, proving same side interior angles are supplementary, showing both lines are parallel to a
third line or by showing both lines are perpendicular to the same line.
Have students prove the following lines are parallel using one of the above methods.
Challenge!There are 13 red and white alternating stripes on the United States Flag. Explain why the top red stripe
must be parallel to the third white stripe.Answer: Using the syllogism property and the idea of parallel lines, since
each lines is parallel to the one before it, then the first red stripe must be parallel to the third white stripe. Also, the
flag may look weird if the stripes were not parallel!
1.3. Parallel and Perpendicular Lines