We don't have just an x here. We have the whole expression that defines u of x. We have u of x right there. And let me draw a little line here so that we don't get those two sides confused. And so we know from the chain rule, the derivative of y with respect to x, this is going to be, this is going to be the derivative of v with respect to u. Or we could call that v prime, v prime of u of x. v prime of u of x. Let me do the u of x in blue.