∫(lnx)dx (令t=lnx) =∫tde^t =te^t-∫e^tdt =te^t-∫2tde^t =te^t-2te^t+∫2e^tdt =te^t-2te^t+2e^t+C(C是任意常数) =(t-2t+2)e^t+C =(lnx-2lnx+2)x+C 原函数是(lnx-2lnx+2)x+C