I can't claim that I would have figured it out on my own, maybe eventually if I were spending hours on it. And I'm assuming somebody was fumbling with it long enough they said, oh wait, wait, look, if I just add and subtract the same term here, I can begin to algebraically manipulate it and get it to what we all know is the classic product rule. So what do I add and subtract here? Well, let me give you a clue. So if we have plus, actually let me change this, minus f of x plus h, g of x. I can't just subtract, if I subtract it, I've got to add it too, so I don't change the value of this expression. So plus f of x plus h, g of x. Now I haven't changed the value, I just added and subtracted the same thing.