V of u of x. V of u of x. Or, another way of writing it, I'm going to write it multiple ways, it's the same thing as v of cosine of x. V of cosine of x. And so v, whatever you input into it, it just takes it to the third power. If you were to write v of x, it would be x to the third power. So the chain rule tells us, or the chain rule is what our brain should say, hey, it becomes applicable if we're going to take the derivative of a function that can be expressed as a composite function like this. So just to be clear, we can write f of x, f of x is equal to v of u of x. I know I'm essentially saying the same thing over and over again, but I'm saying it in slightly different ways because the first time you learn this, it can be a little bit hard to grok, or really deeply understand. So I'm going to try to write it in different ways.