令arctanx=u则x=tanuf'(u)=(tanu)^2=(secu)^2-1f(u)=tanu-u+c所以 f(x)=tanx-x+c
f'(arctanx)=x^2df(arctanx ) = x^2 dxf(arctanx )=(1/3)x^3 + C'f(x) = (1/3) (tanx)^3 + C
