令t=三次根号下x,则x=t³,dx=3t²dt
所以原式=3∫t²/(1+t)dt=3∫[(1+t-1)²/(1+t)dt
=3∫[1+t+1/(1+t)-2]dt
=3[-t+1/2t²+ln(1+t)]+C
其中t=三次根号下x
x^(1/3)=t x=t^3,dx=3t^2dt
∫1/(1+t)dx
=∫3t^2dt/(1+t)
=3∫(t^2-1+1)dt/(1+t)
=3∫(t-1+1/(1+t))dt
=3(t^2/2-t+ln(1+t))+C
=3(x^(2/3)/2-x^(1/3)+ln(1+x^(1/3)))+C