f'(x)=1/(ex/2)*(e/2)-f'(1)
=1/x-f'(1)
令x=1
f'(1)=1-f'(1)
f'(1)=1/2
f'(x)=1/x-1/2
f'(2)=0
f'(x)=1/x-1/2
定义域x>0
0