Slope is the angle at which a line differs from the horizontal. On a coordinate plane, slope is defined as change in y, divided by change in x, also known as rise over run.
Choose two points
A straight line always has the same slope no matter how much of it considered. For convenience, find two points where the line intersects the coordinate plane at easy-to-read points rather than between whole numbers.
Subtract one y coordinate from the other y coordinate
If you chose the points (0, 3) and (3, -3), for example, begin by finding the difference between the two y coordinates. In this case, the answer is either 6 or -6, depending on which order you perform the operation. As long as you perform the operation in the same order when you find the difference between x coordinates, this difference does not matter.
Subtract one x coordinate from the other x coordinate
If you subtracted 3 from -3 to find the value for change in y, subtract 0 from 3 to find the change in x. If you originally subtracted -3 from 3 to find the change in y, then subtract 3 from 0 to find the change in x.
Divide change in y by change in x
Depending on the order you chose, you are either dividing -6 by 3, or 6 by -3. In either case, the answer is -2. This is the slope of the line. In the standard form for a linear equation, y = mx + b, m stands for the slope.