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. Let's do x squared times sine of x. We could have done it either way. And we are curious about taking the derivative of this.