So let's take the derivative of this. So we can view this as the product of two functions. So the product rule tells us that this is going to be the derivative with respect to x of e to the cosine of x, e to the cosine of x times cosine, times cosine of e to the x plus, plus the first function, just e to the cosine of x, e to the cosine of x times the derivative of the second function, times the derivative with respect to x of cosine of e to the x, cosine of e to the x. And so we just need to figure out what these two derivatives are. And so you can imagine the chain rule might be applicable here. So let me make it clear. This we got from the product rule.