∫∫x/ydxdy=∫[0,2a](1/y)dy ∫[0,√(2ay-y^2)] x dx 注：∫[a,b]表示从a到b的积分.而∫[0,√(2ay-y^2)] x dx=x^2/2|[0,√(2ay-y^2)]= (2ay-y^2)/2∫∫x/ydxdy=∫[0,2a](1/y) (2ay-y^2)/2dy=(1/2)∫[0,2a](2a-y)dy=...