Subtract the y-coordinates: -2 - 3 = -5
Subtract the x-coordinates in the same order: 1 - 1 = 0
slope = (difference in y)/(difference in x) = 5/0
Since the slope ends up as division by zero, and division by zero is undefined, the slope of this line is undefined.
Hint for future:
Vertical line: undefined slope
Horizontal line: zero slope
Line tilts up to the right: positive slope
Line tilts down to the right: negative slope