答：
∫(x^3-2x)/(1+x^4)dx
=∫x^3/(x^4+1)dx-∫2x/(1+x^4)dx
=(1/4) ∫1/(x^4+1)d(x^4) - ∫1/(x^4+1)d(x^2)
=(1/4)ln(x^4+1) - arctan(x^2)+C