If I had some function f of x is equal to cosine of x times sine of x, it would be hard to express this as a composition of functions, but I can represent it as the product of functions. For example, I could say cosine of x, I could say u of x is equal to cosine of x, and I could say v of x, let me use a different color, I could say v of x is equal to sine of x. And so here, f of x wouldn't be the composition of u and v, it would be the product. F of x is equal to u of x times v of x, v of x. If we were to take the composition, if we were to say u of v of x, pause the video, think about what that is, and that's a little bit of a review. Well, this is going to be, I take u of x, takes the cosine of whatever is input, and now the input is v of x, which would be sine of x. Sine of x.