For a lesson on how, in general, to find area with polar coordinates, try
here.
From
the graph, you know that the limits for this curve will be 0 and
. The integral will then be:
. . . . .By symmetry, this can be simplified a bit to:
. . . . .. . . . .By applying
some trig identities, you should be able to get:
. . . . .Then apply the standard trig-integral identity:
. . . . .Integrate, evaluate, and you should be done!