Undefined 
Slope is equal to the change in 
y
y
 over the change in 
x
x
, or rise over run.
The change in 
x
x
 is equal to the difference in x-coordinates (also called run), and the change in 
y
y
 is equal to the difference in y-coordinates (also called rise).
Substitute in the values of 
x
x
 and 
y
y
 into the equation to find the slope.
The expression contains a division by 
0
0
 The expression is undefined.