Line EF has an equation of a line y = −2x + 7. Which of the following could be an equation for a line that is perpendicular to line EF?

y = 2x − 3
y = 1 over 2x − 3
y = −2x − 3
y = −1 over 2x − 3

Question

Line EF has an equation of a line y = −2x + 7. Which of the following could be an equation for a line that is perpendicular to line EF?

 y = 2x − 3
 y = 1 over 2x − 3
 y = −2x − 3
 y = −1 over 2x − 3

directrix · Answer

Perpendicular lines (provided neither is vertical) have slopes that multiply to -1.

If the given line has a perpendicular line to it among the options, the option line will have a slope of 1/2 because the given line's slope is -2 and -2 times 1/2 = -1.