We will also see equations whose graphs are vertical lines. These are graphs in which
* x*
remains constant -- that is, in which
* x*
1 - * x*
2 = 0
for any two points on the line:

Graph of a Vertical Line
* m* = = = undefined
. We cannot divide a number by zero.

The slope of any vertical line is undefined.
* x*
does not increase or decrease; rather,
* y*
takes every possible value at a specific
* x*
value.