dy/dx, ie., the difference in y divided by the difference in x. If you have two points A and B, sort them in ascending order of x.
dx = 5 - -3 = 8 (x coordinates of B minus x coordinate of A)
dy = -3 - 5 = -8 (y coordinate of B minus y coordinate of A)
dy/dx = -1
So the slope is -1. The equation of the line is y=2-x.
