y=f(e^cos√x)

y'=f'(e^cos√x)*(e^cos√x)*(-sin√x)/(2√x)
x趋向于0+
limy'
=limf'(e^cos√x)*(e^cos√x)*(-sin√x)/(2√x)
=f'(e)e(-1/2)
=e/2