求不定积分 1.∫ x/(1+（x^2))dx 2.∫cos^2 x sinx dx

∫ x/(1 + x²) dx
= ∫ d(x²/2)/(1 + x²)
= (1/2)∫ d(x² + 1)/(1 + x²)
= (1/2)ln(1 + x²) + C
∫ cos²x•sinx dx
= ∫ cos²x d(-cosx)
= -∫ cos²x d(cosx)
= (-1/3)cos³x + C