1. Lesson 6.5 Parallel and Perpendicular Lines
Objective: To determine whether lines are parallel or perpendicular.

2. Check Skills You’ll Need
What is the reciprocal of each fraction?
4/3
-2/5
-7/5
1 2/3

3. Check Skills You’ll Need (continue)
What are the slope and y-intercepts of each equation?
y = 5/3x + 4
y = 5/3 x – 8
y = 6x
y = 6x + 2
y = -1/4x -1
y = 4x + 2

4. Vocabulary
Parallel lines are lines in the same plane that never intersect. Nonvertical lines are parallel if they have the same slope and different y-intercepts. Any two vertical lines are parallel.
Perpendicular lines are lines that intersect to form right angles. Two lines are perpendicular if the product of their slopes is -1. A vertical and a horizontal line are also perpendicular. The product of two numbers is -1 if one number is the negative reciprocal of the other.

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6. Writing Equations of Parallel Lines
Write an equation for the line that contains (2, -6) and is parallel to y = 3x + 9.

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9. Write an Equation for Perpendicular Lines
Find an equation of the line that contains (6,2) and is perpendicular to y = -2x + 7.

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