Question 14452
You will usually see the formula for the slope of a line, when you are given two points, written as:

{{{m = (y2 - y1)/(x2 - x1)}}} Where the coordinates of the two points are: (x1, y1) and (x2, y2)

In this problem, the two given points have the coordinates: (a, b) and (c, d), so the slope formula would look like:

{{{m = (d - b)/(c - a)}}}

And, in order to not run into the undefined situation of division by zero, we cannot have a = c, otherwise you would have:

{{{m = (d - b)/0}}} and this is not defined.