And on the right-hand side, you're going to have the derivative of cosine y with respect to y, which is negative sine of y times the derivative of y with respect to x, which is dy dx. And so we get, let's see, if we divide both sides by negative sine of y, we get dy dx is equal to negative one over sine of y. Now, like we've seen before, this is kind of satisfying, but we have our derivative in terms of y. We want it in terms of x. And we know that x is cosine of y. So let's see if we can rewrite this bottom expression in terms of cosine of y instead of sine of y. Well, we know, and we saw it in the last video, that from the Pythagorean identity, that cosine squared of y plus sine squared of y is equal to one.