Download Lesson 3.9 AIM: Parallel and Perpendicular Lines

Lesson 3.9
AIM: Parallel and
Perpendicular Lines
DO NOW: Turn into slope intercept form.
5x - y = 6
-5x
-5x
- y = -5x + 6
- 1 -1 - 1
y = 5x - 6
Graph y = 2x + 2
and y = 2x - 3
Graph y = 2x + 3
and y = (-1/2)x + 2
What do parallel lines have in
common?
• They have the same slope!
(and different y-intercepts)
• Given line: y = 2x - 3
• Parallel line: y  2x  4
• Given line: y = -4x + 2
• Parallel line: y  4 x

3
How are slopes of
perpendicular lines related?
• Take the negative reciprocal of the slope.
(you can have the same or different y-intercept)
• Given line: y = 3x - 5
1
• Perpendicular line: y   x  5
3
2
3
• Given line: y   x  6
 line: y  3 x  6
• Perpendicular
2
• Given
 line: y 
1
x4
7
 line:
• Perpendicular
y  7x  4
Summary Question
Write the equation of a line parallel to
2x + 3y = 12.
(hint: turn your equation into slope intercept form)