And all it tells us is that if we have a function that can be expressed as the product of two functions, so let's say it can be expressed as f of x times g of x, and we want to take the derivative of this function, we want to take the derivative of it, that it's going to be equal to the derivative of one of these functions, f prime of x, let's say the derivative of the first one, times the second function, plus the first function, not taking its derivative, times the derivative of the second function. So here we have two terms. In each term, we took the derivative of one of the functions and not the other. And we multiply the derivative of the first function times the second function plus just the first function times the derivative of the second function. Now let's see if we can actually apply this to actually find the derivative of something. So let's say we are dealing with x squared times cosine of x. Or let's say, well, yeah, sure.