12.3#8 again.

Hi Dr. Taylor, I can't seem to get this one, I've tried entering   f(rcos(t),rsin(t) as well.

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OK, you and a lot of people are making this harder than it has to be.  Still.  First of all, the only answer is doesn't like is the one about dA. It's not talking about f at all, so you don't have to worry about that.  There is a formula for dA in polar coordinates, I talk about it in my lecture notes, I talked about it about ten times in my video lecture last week that is still online, and the book talks about it in section 12.3. It is the single most important thing for you to know about polar integration. This formula DOES NOT DEPEND ON the limits of integration--that's one nice thing about it. WHAT IS THIS FORMULA?