Perpendicular Lines

Perpendicular Lines

Parallel Lines are lines that never intersect. Perpendicular Lines are lines that intersect at right angles.

Slopes of Perpendicular Lines

The slopes of perpendicular lines are "negative reciprocals"

example:

 $m\ =\frac{2}{3}$   and  $m\ =\ \frac{-3}{2}$  
They must be reciprocals and one is positive and the other is negative.

The following slopes are not perpendicular...

• m = 5 and m =1/5 (they are only reciprocals)

• m = 3 and m = -3 (they are only opposites)

Ready to try some examples?

Remember the slopes are "negative reciprocals"

Multiple Choice

Slopes of perpendicular lines are...

• negative reciprocals.

• opposites.

• the same.

• always 7.

Multiple Choice

Are the two lines perpendicular?

y = 3x + 4 and y = 1/3x - 2

• Yes

• No

Multiple Choice

Are the two lines perpendicular?

y = -3/4x + 2 and y = 4/3x - 1

• Yes

• No

Multiple Select

Which two slopes would be perpendicular to each other?

• m = 1/2

• m = -1/2

• m = 2

Multiple Choice

Which line is perpendicular to the line y = 4x - 2?

• y = 4x + 5

• y = 1/4x + 2

• y = -4x - 3

• y = -1/4x + 4