slope of (C) is – , or –6; and the slope of (D) is – , which equals –3. So, (D) is the correct
answer.
Parallel and Perpendicular Lines
So now we know that parallel lines have the same slope. Whenever the SAT brings up perpendicular
lines, just remember that a perpendicular line has a slope that is the negative reciprocal of the other line’s
slope. For instance, if the slope of a line is 3, then the slope of a line perpendicular to it would be – .
Combine this with the skills you’ve already learned to attack a problem about perpendicular lines.
Parallel vs.
Perpendicular
Parallel lines have the
same slope and never
intersect. Perpendicular
lines have slopes that are
negative reciprocals and
intersect at a right angle.Here’s an example:
18.Which of the following is the graph of a line perpendicular to the line defined by the
equation 2x + 5y = 10 ?