Question 40613
Find the slope of the line through the pair of points.
(-9, -6) and (-9, -8)
When finding the slope of a line (m) passing through 2 points (-9, -6) and (-9, -8) we can use the slope formula.
{{{m=(y2-y1)/(x2-x1)}}}
Lets use point (-9,-6) as (x1,y1) and point(-9,-8) as (x2,y2).
{{{m = (-8-(-6))/(-9-(-9))}}}
This means...
{{{m = (-8+6)/(-9+9)}}}
Then perform the indicated operations...
{{{m = (-2)/(0)}}}
Which is undefined.
The slope formula gives us a fraction that tells us the value of the slope m.
{{{m=rise/run}}}
The rise tells us how a line moves verticaly on a graph, and the run tells us how a line moves horizontaly on the same graph.
So if the rise is -2 and the run is 0 then we know that the line does not move horizontaly, or it is a vertical line.
So the slope is undefined. 
I hope this helps.
Good Luck!