So there you have it. The derivative with respect to x of the inverse cosine of x is, I think I lost that color, I'll do it in magenta, is equal to negative one over the square root of one minus x squared. So this is a neat thing. This right over here is a neat thing to know. And of course, we should compare it to the inverse, the derivative of the inverse sine. Actually, let me put them side by side, and we see that the only difference here is the sine. So let me copy and paste that.