I think the correct formula is .

To do the integral, you'll need the identity .

To check your answer, the result should be roughly the area of a circle with radius 2, which, of course, is .

- Hollywood

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- April 22nd 2010, 03:30 PM #1

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- April 23rd 2010, 11:01 PM #2

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- April 24th 2010, 03:43 AM #3

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- April 24th 2010, 05:16 PM #4

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If you look at a small piece of the graph, it is a sector of a circle (the shape of a slice of pie). The angle at the origin is , and the radius is . Since the angle at the origin for a whole circle is , our wedge shape is of a circle. Since the area of a circle is , the area of the wedge is . That explains the integrand.

Our curve is traced by going from 0 to , so that explains the limits of integration.

- Hollywood