I'm trying to find the area of one petal of r=2cos(3θ). I tried to integrate the area of the whole graph and then divide it by 3 but it doesn't seem to work.

When I tried to find points where r=0, I don't know what values of θ to use because I wasn't sure which two angles would give the area of exactly one petal. (I was worried that I might get an area of two petals or two and a half or something like that.)

Can someone help me to approach this problem please?

Thanks!