And the best way that I can think about doing that is by taking the derivative of both sides of this equation. So let's take the derivative of both sides of that equation. So the left-hand side, we'll take the derivative with respect to x of g of x, and the right-hand side, the derivative with respect to x of all of this business. Now the left-hand side is pretty straightforward. The derivative with respect to x of g of x, that's just going to be g prime of x. But what is the right-hand side going to be equal to? Well, that's where the second fundamental theorem of calculus is useful.