Question

Which line is perpendicular to y=2x+5?

(A) y=5x+2
(B) y=2x-4
(C) y=1/2x+1
(D) y=-1/2x+5

Answer 1

y = mx + n

m = Slope

To two lines be perpendicular to each other the slopes need to meet the condition: ma x mb = -1

y = 2x + 5
ma = 2

D: y = -1/2x + 5
mb = -1/2

ma x mb = -1

2 x -1/2 = -1
2/1 x -1/2 = -1
-2/2 = -1
-1 = -1

It's true.

Answer: D.