http://www.ck12.org Chapter 3. Parallel and Perpendicular Lines
Solution:
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 4:What is the slope of the line through (3, 2) and (3, 6)?
Solution:
m=6 − 2
3 − 3
=
4
0
=unde f inedTherefore, the slope of this line is undefined, which means that it is averticalline. Verticallines always pass through
thex−axis. Notice that thex−coordinate for both points is 3. In fact, thex−coordinate foranypoint on this line is
- This means that the vertical line must crossx=3.