So let's see if we can find the derivative with respect to x of e to the x times cosine of x. And like always, pause this video and give it a go on your own before we work through it. So when you look at this, you might say, well I know how to find the derivative with respect of e to the x. That's in fact just e to the x. And let me write this down. We know a few things. We know the derivative with respect to x of e to the x. E to the x is e to the x.