Let's take the derivative with respect to x of both sides of this, derivative with respect to x. The left side here, well, this will just become whatever's inside of the indefinite integral. This will just become f of x plus g of x, plus g of x. Now, what would this become? Well, we could just go to our derivative properties. The derivative of the sum of two things, that's just the same thing as the sum of the derivatives. So this will be a little bit lengthy.