Times dy dx. And the right-hand side, what's the derivative of x with respect to x? Well, that's obviously just going to be equal to 1. And so we could solve for dy dx, divide both sides by cosine of y, and we get the derivative of y with respect to x is equal to 1 over cosine of y. Now, this still isn't that satisfying because I have the derivative in terms of y. So let's see if we can re-express it in terms of x. So how could we do that?