To find the slope going from (-5,-3) to (-5,2) we are going to calculate the change in y over the change in x, or the rise over the run. The change is the difference between the two coordinates. So if the y-coordinate of a point goes from -3 to 2, the change in these numbers is 5 (since  ). If the x-coordinate changes from -5 to -5, then the change is 0 (since  ). So to calculate the slope we use this formula:
Slope:
 where m is the slope
So now we let  , , , Now plug these numbers into the slope formula:
 Since the two points have the same x-coordinate, we have a denominator of zero. Remember we cannot divide by zero. In other words, this is not possible:  (we cannot divide any number by 0) This means the slope is undefined, and because we don't have any change in x, we have a vertical line at x=-5 |
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