1，为什么∫（x3/x2+1）dx=1/2∫（x2/x2+1）dx2,详细一点∫(x3/x2+1)dx凑微分！=∫(1/2*2x*x2/x2+1)dx=1/2∫(2x)*(x2/x2+1)dx因为dx2=2xdx=1/2∫(x2/x2+1)dx2∫[x3/(x2+1)]dx=∫[x2·x/(x2+1)]dx=(1/2)∫[x2/(x2+1)]d(x2)——因为d(x2)=2xdx！！！∫[x/(x+1)]dx=∫[x·x/(x+1)]dx=(1/2)∫[x/(x+1)]d(x)——因为d(x)=2xdx！