We could take the derivative of both sides with respect to x. So derivative of the left-hand side with respect to x and the derivative of the right-hand side with respect to x. Well, what's the derivative of the left-hand side with respect to x going to be? And here we just apply the chain rule. It's going to be the derivative of sine of y with respect to y, which is going to be cosine of y times the derivative of y with respect to x. So times dy dx. Times dy dx.