∫ t²/(1 + t) dt= ∫ t(t + 1 - 1)/(1 + t) dt= ∫ t dt - ∫ t/(1 + t) dt= t²/2 - ∫ (t + 1 - 1)/(1 + t) dt= t²/2 - ∫ dt + ∫ dt/(1 + t)= t²/2 - t + ln|1 + t| + C___________________...= ∫ d(x²/2)/(1 - x²)= (-1/2)∫ d(1 - x²)/(1 - x²)这2步怎么相等的，我不会算d(x²/2) = (1/2)d(x²) = (1/2)d[(-x²)/(-1)] = (1/2)(-1)d(-x²) = (-1/2)d(-x²) = (-1/2)d(-x² + 1)= (-1/2)d(1 - x²)逐步凑微分