x*(2rx-x^2)^1/2dx=1/2{(2r-2x)(2rx-x^2)^1/2}dx-r*(2rx-x^2)^1/2dx=1/2(2rx-x^2)d(2rx-x^2)-r*(2rx-x^2)^1/2dx第一个就没问题了吧!积分1/2(2rx-x^2)d(2rx-x^2)=1/4(2rx-x^2)^2第二个：因为：2rx-x^2=-(x-r)^2+r^2=r...