2-4 standardized test prep

Question

Which equation represents a line through (- 2, 1) that is perpendicular to y=-5x+2?

(A) y = 1/5 * x + 7/5

(B) y = - 5x - 9

(C)y = - 1/5 * x - 7/5

(D) y = 5x + 9

Answer 1

Perpendicular lines have opposite, reciprocal slopes. Which equation has the opposite, reciprocal slope of your equation and has (-2,1) as a solution (meaning you plug both points in and it makes the equation true)?

For example...

Is (3,1) on y = 2x + 6?

1 = 2(3) + 6

1 = 6 + 6

1 = 12

0 = 11

Since that's not true, (3,1) is not on the given line.

Answer 2

the slope of the perpendicular MUST be 1/5

option A is the only one having that slope

note that (1/5)(-2) + 7/5 = -2/5 + 7/5 = 1, so (-2,1) is on it

clearly option A: y = (1/5)x+7/5