答:
f(x)=lnx-x+2,x>0
f'(x)=1/x-1
解f'(x)=1/x-1=0得:x=1
00
x=3时,f(3)=ln3-3+2=ln3-1>0
x=4时,f(4)=ln4-4+2=ln4-2