（d/dx)f(e^cos√x)
=f‘(e^cos√x)*e^cos√x*sin√x*(1/2√x)
所以：lim(x→0+)(d/dx)f(e^cos√x)
=lim(x→0+)f‘(e^cos√x)*e^cos√x*(-sin√x)*(1/2√x)
=-f‘(e)e/2
=e(e^(-1))
=1