In other words, change in y over change in x. Now once again, if our A equals one, then when we graph this equation on the XY plane, we should get a negative slope like this a straight line. Now, suppose our A was zero, and we tried graphing this equation the same way. Then since A equals zero, this would not be a straight line, it'd be some other line. And that means we can conclude that our A is not one, our A must be something else. And in order to determine A equals zero, we have to actually graph what we graphed before and after we graph.