原式=∫ln(1-x)d(1-x)
=(1-x)ln(1-x)-∫(1-x)dln(1-x)
=(1-x)ln(1-x)-∫(1-x)*[-1/(1-x)]dx
=(1-x)ln(1-x)+∫dx
=(1-x)ln(1-x)+x+C