1. Perpendicular Slope & Equation of Perpendicular Lines
Lesson 5-8

2. Math Vocabulary
Perpendicular Lines: two lines on a graph, that DO intersect, forming a right angle, based on opposite slope

3. Finding Parallel Slope…
Perpendicular Lines have… The opposite/reciprocal slope! If y = 3/5 x – 4 m = 3/5 then perpendicular slope  perpendicular m = - 5/3

4. Finding Parallel Slope…
Find the slope of a line perpendicular to the equation… y = -5 x – 3 m = -5  perpendicular m = 1/5
Find the slope of a line perpendicular to the equation… x – 3y = 7 *Needs to be in y = mx + b -x -x -3y = -x y = 1/3 x – 7/3 m = 1/3 perpendicular m = - 3

5. Finding Perpendicular Slope…
Find the slope of a line perpendicular to the equation… y = -4x + 7 m = -4 perpendicular m = ¼
Find the slope of a line perpendicular to the equation… 3y + 6x = 12 *Needs to be in y = mx + b m = -2 perpendicular m = ½

6. Equation of a line with Perpendicular Slope…
Finding the equation of a line perpendicular to y = -4x + 1 AND… that passes thru the point (-8, 0) 1) Name the current slope m = -4 2) Name the perpendicular slope perpendicular m = 1/4
2) Solve to write the equation with…
m = 1/4, thru (-8, 0)
y = mx + b
0 = ¼ (-8) + b
0 = -8/4 + b
0 = -2 + b
2 = b
Eq.  y = ¼ x + 2

7. Practice…
Find the parallel & perpendicular slope of each equation of a line…
y = - 8/3x parallel m =
perp m =
15x + 3y = -3 parallel m =
Write the equation of a line perpendicular to
y = -2x + 1, and that passes thru (-4, 3)

8. Homework
p #13-17, 21-23, 42, 43