令t= √u
则u=t^2
du=2tdt
原式=∫(sint)^2 *2tdt
=∫t(1-cos2t)dt
=∫t-∫tcos2tdt
=t^2/2-[ t*0.5sin2t-∫0.5sin2tdt]
=t^2/2-t/2* sin2t-0.25cos2t+C
=u/2- √u /2*sin(2 √u)-0.25cos(2 √u)+C