用凑微分∫xtanx(secx)^4dx=∫xtanx([(tanx)^2+1]dtanx=∫x(tanx)^3dtanx+∫xtanxdtanx=(1/4)∫xd(tanx)^4+(1/2)∫xd(tanx)^2=(1/4)[x(tanx)^4-∫(tanx)^4dx]+(1/2)[x(tanx)^2-∫(tanx)^2dx].(*)因为∫(tanx)^4dx=∫...