设f(√x)=arctanx,则f(x)=_____.

设f(√x)=arctanx,则f(x)=_____.
【正确答案】:2x/(1+x4) 分析:令√x=t,则x=t2,f(t)=arctant2所以f'(x)=(arctanx2)′=2x/(1+x4)