http://www.ck12.org Chapter 3. Parallel and Perpendicular Lines
Example B
Find the slope between (-8, 3) and (2, -2).
m= 2 −−^2 (−−^38 )=− 105 =−^12
This is a negative slope.
Example C
Find the slope between (-5, -1) and (3, -1).
m=− 1 −(− 1 )
3 −(− 5 )
=
0
8
= 0
Therefore, the slope of this line is 0, which means that it is a horizontal line. Horizontallines always pass through
they−axis. Notice that they−coordinate for both points is -1. In fact, they−coordinate foranypoint on this line is
-1. This means that the horizontal line must crossy=−1.
Example D
What is the slope of the line through (3, 2) and (3, 6)?
m=6 − 2
3 − 3
=
4
0
=unde f inedTherefore, the slope of this line is undefined, which means that it is a verticalx−axis. Notice that thex−coordinate
for both points is 3. In fact, thex−coordinate foranypoint on this line is 3. This means that the vertical line must
crossx=3.
Watch this video for help with the Examples above.
MEDIA
Click image to the left for more content.CK-12 Foundation: Chapter3SlopeintheCoordinatePlaneB
Vocabulary
Slopeis the steepness of a line. Two points(x 1 ,y 1 )and(x 2 ,y 2 )have a slope ofm=((xy^22 −−yx^11 )).
Guided Practice
Find the slope between the two given points:
- (3, -4) and (3, 7)