Question

y=(arctanx)^2,求x=0时y的n阶导数

Answer 1

y=(arctanx)^2
y'=2arctanx*(arctanx)'
=2arctanx*[1/(x^2+1)]
=2arctanx/(1+x^2).
y''=[2/(1+x^2)(1+x^2)-2arctanx*2x]/(1+x^2)^2
=2(1-2xarctanx)/(1+x^2)^2