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...