This document provides examples and explanations of parallel and perpendicular lines. It defines parallel lines as having the same slope and perpendicular lines as having negative reciprocal slopes. It then gives three example problems determining whether lines defined by equations are parallel or perpendicular based on comparing their slopes.

1. 2

2. Parallel lines have the same slopes so
find the slope of the given line and the
slope you want for a parallel line will be
the same.
Perpendicular lines have negative reciprocal
slopes. Take the slope of the given line,
switch the numerator and denominator and
change the sign for the slope of its
perpendicular line.
Parallel & Perpendicular Lines:

3. Practice Problems:

6. EXAMPLE 2
Determine whether lines are parallel or perpendicular
Line a: y = 5x – 3
Line b: x + 5y = 2
Line c: –10y – 2x = 0
SOLUTION Find the slopes of the lines.
Line a: The equation is in slope-intercept form.
The slope is 5.
Write the equations for lines b and c in slope-intercept
form.

7. EXAMPLE 2:
Line b: x + 5y = 2 5y = – x + 2
Line c: –10y – 2x = 0 –10y = 2x y = – x1
5
Determine whether lines are parallel or perpendicular
xy =
2
5
1
5 +–

8. Determine which lines, if any, are parallel or perpendicular.
Line a: 2x + 6y = –3
Line b: y = 3x – 8
Line c: –1.5y + 4.5x = 6
ANSWER
parallel: b and c; perpendicular: a and b, a and c

9. Class Work:
3.1
Front is review of Coordinate Plane Unit
Reverse is parallel & perpendicular lines