Slope is the change in y divided by the change in x, also known as rise over run. The formula is (y2 - y1) / (x2 - x1). The order may be reversed, and as long as you are consistent, you will get the same result. So the numbers work out to
(1 - (-4)) / (-10 - 0) = 5 / -10 = -1 / 2
