Perpendicular Lines

Question

Which equation describes the line that passes through the point (-9,9) and is perpendicular to the graph of y=-8/9x-4/9?

 

a. y=9/8x + 153/8

b. y= -9/8x - 9/8

c. y=9/8x -9/8

d. y=-9/8x - 153/8

 

Answer 1

Perpendicular lines have inverse, negative (opposite) slopes, so you can eliminate b and d

Now plug in the point (-9,9) to the other two equations to find out which has that point.

A
y = 9/8 x + 153/8

9 = 9/8(-9) + 153/8

9 = -81/8 + 153/8

9 = 72/8

YES

C
y = 9/8 x - 9/8
9 = 9/8(-9) -9/8

9 = -81/8 - 9/8

9 = -90/8

NO

THE ANSWER IS A