But if you did a little experimentation, you would realize that whenever you expand a plus b to the nth power, the first term is going to be a to the n. And then the second term is going to be plus n a to the n minus 1 b. And then you could keep having a bunch of terms. But these are the only terms that are relevant in this proof, because all the other terms get canceled out when delta x approaches 0. So if you just knew that, you could have done this. But it's much better to do it with the binomial theorem. Ignore what I just said if it confused you. I'm just saying that we could have just said, oh, the rest of these terms just all go to 0.