f(x)=∫xsinxdx =-∫x dcosx =-xcosx+∫sinxdx =-xcosx-cosx+c(常数)用的是分部积分法。
f(x) =∫xsinx dx=-xcosx+∫cosx dx=-xcosx+sinx+c
f(x)=sinx-xcosx
