Since the x coordinates of the two points are both the same (x = 5), this means the two points line up to form a vertical line. All vertical lines have undefined slopes.
We can see this through the use of the slope formula m = (y2-y1)/(x2-x1) m = (-2-3)/(5-5) m = -5/0 we cannot divide by zero. Dividing by zero is undefined. That's why the slope is undefined.