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!