x=tant,t=arctanx,dx=(sect)^2dt
积分号(x的立方/(1加x平方)的3/2次方)dx
=S((tant)^3/(sect)^3*)(sect)^2dt
=S(tant)^3/sect dt
=S(sint)^3/(cost)^2dt
=-S(sint)^2/(cost)^2dcost
=-S(1-(cost)^2)/(cosx)^2dcost
=-S(cost)^(-2)dcost+Sdcost
=1/cost+cost+c
=根号（x^2+1)+1/根号（x^2+1)+c