Well, what's the radius of the inside squared? Well, the inside, in this case, is g of x. It's going to be pi times g of x squared. That's the inner function, at least over the interval that we care about. So the area of this washer, we could just leave it like this, or we could factor out a pi. We could say it's equal to the area is equal to, if we factor out a pi, pi times f of x squared, f of x squared minus g of x squared. Minus, I don't, I have to write a parentheses there.