And then u prime of x, we already figured out is negative one, so I could write times negative one. Well, yeah, let me just leave it out there for now. I could have just put a negative out front, but I really want you to be able to see what I'm doing here. So now we want to evaluate at x equals pi over four. So when that is equal to pi over four, pi over four. So let's see, this is going to be, this is going to be equal to sine of, what's three pi over two minus pi over four? I'll do that over here.