So now let's start with y equals mx plus b. So if y is equal to mx plus b, y equals mx plus b, so this is the equation of a line, then dy dx is going to be equal to, well the derivative of this with respect to x is just m, derivative of this with respect to x, it's a constant, it's not going to change with respect to x, it's just a zero. And that makes sense. The rate of change of y with respect to x is the slope of our line. So can we use, and this is really all that we know, we could keep, actually we could go even further. We could take the second derivative here. The second derivative of y with respect to x, well that's going to be zero.