Hi, my name is Bassem Saad. I'm a Math Ph.D. candidate at U.C. Davis, and I'm here today for About.com to show you how to use the slope formula. A slope is an important feature on any line and can be calculated in a straight-forward way. Let's take a look at an example.These are the coordinates of two points on a line. We can calculate the slope by writing out the change of y on top -- that is, minus three, minus one; and the change of x on the bottom -- that is, seven minus three. Now we have minus four over four, which is just negative one.Now let's take a look at a word problem: Suppose a car is traveling at a constant speed, but we don't know how fast it's actually going. Instead, we know that the car has traveled 180 miles after three hours. We can calculate how fast it's going by using the slope formula.All we need are the coordinates for the two points. Our first point is zero, zero, because at time zero the car hasn't moved. Our second point is three and 180, because after three hours, it's traveled 180 miles. Then the slope (m) equals the change of y, which is just 180 miles minus zero, which is 180 miles; divided by the time, which is three hours minus zero, which is just three hours. You're left with 60 miles per hour.As we've seen, the slope can be used to approximate the speed of moving objects. It can also be used to approximate the margin of revenue for a business, or the relationship between the compression of a spring and the force it exerts. Thanks for watching, and to learn more, visit us on the web at About.com.