f(x)=x-lnx,x属于(0,+∞)f'(x)=1-1/x令f'(x)=0,解得x=1(0,1)递减,(1,+∞)递增x=1时,有极小值f(1)=1 lim(x趋近于0）f(x)=+∞lim(x趋近于+∞）f(x)=+∞所以最小值为1,无最大值.(2)f'(x)=a-1/x, x属于(0,+∞)当a≤0时,f...