1. Parallel and Perpendicular Lines
5-6

2. Parallel Lines Parallel lines do not intersect!
y = 2x and y = 2x + 3 will be parallel.
Parallel lines will have the same slope and different y-intercepts.

3. Parallel Lines
y = 2x and y = 2x + 3 will be parallel.

4. Parallel Lines
Write the slope-intercept form of an equation for the line that passes through (-1,-2) and is parallel to the graph of y = -3x -2. THE SLOPE OF BOTH EQUATIONS WILL BE -3.
y = mx + b (-1,2) SLOPE = -3
-2 = -3(-1) + b
-2 = 3 + b
-3 = -3
- 5 = b The equation is: y = -3x -5

5. Example 2
Write the slope-intercept form of an equation for the line that passes through (4,-2) and is parallel to the graph of y = 1 x -7 2
( The slope will be 1 )

6. Parallel Lines
Write an equation of the line containing the point (0,6) and parallel to the line: The slope will be -3
y = -3x + 4

7. Perpendicular Lines
Perpendicular lines intersect and form rt. angles. The product of the slopes is -1.
Ex if a slope is -3, then the other slope of the line is 1
BECAUSE:
-3 * 1 = -1

8. Perpendicular Lines If a slope is -1 the line perpendicular 4
to that line must be 4 because:
-1 * 4 = = -1

9. Perpendicular Lines
Write the slope-intercept form of an equation that passes through (-2, 0) and is
perpendicular to the graph of y = x -6
Slope of equation is 1, New slope must be
-1 because 1 * -1 = -1
y = x -6
0 = -1(-2) + b
0 = 2 + b
b = -2
Equation: y = -1x – 2 or y = -x -2

10. Perpendicular Lines
Write the slope-intercept form for an equation for the line that passes through
(-1,3) and is perpendicular to 2x + 4y = 12
Solve for y in terms of x: 2x + 4y = 12
b) Substitute values in for x, y, and m

11. Practice
Write the slope-intercept form of an equation of the line that passes through the given point and is ll to the graph of the equation.
(3,2), y = 3x ) (-1,-2) y = -3x + 5

12. Practice
Write the slope-intercept form of an equation of the line that passes through the given point and is ll to the graph of the equation.
3) (3,2), y = 3x ) (-5,-1), 2y = 2x -4

13. Practice
Write the slope-intercept form of an equation of the line that passes through the given point and is perpd.( l ) to the graph of each equation.
5) (-3,-2), y = x ) (4,-1), y = 2x -4

14. Practice
Write the slope-intercept form of an equation of the line that passes through the given point and is l to the graph of each equation.
(-5,1), y = - 5 x ) (-2,2) 6x + 3y = -9 3

15. Guided Practice
See pg 295 #4