f'(x)=lnx+1+1/x-a
(1)a=4æ¶ï¼
f(1)=0
f'(1)=-2
â´å线æç为-2ï¼
â´å线æ¹ç¨ä¸ºy-0=-2(x-1)
å³ï¼y=-2x+2
(2)xâ(1ï¼+â)æ¶ï¼f(x)ï¼0
â´é¦å
ï¼å¿
é¡»f'(1)=2-aâ¥0
ãå¦åï¼å¨xç¥å¤§äº1çæ¶åï¼
f(x)ï¼f(1)=0ã
â´aâ¤2
ä¸é¢ï¼æ们è¯æaâ¤2æ¶ï¼
满足xâ(1ï¼+â)æ¶ï¼f(x)ï¼0
令g(x)=lnx+1+1/x-a
aâ¤2æ¶ï¼g(1)=2-aâ¥0
g'(x)=1/x-1/x²=(x-1)/x²
xâ(1ï¼+â)æ¶ï¼g'(x)ï¼0
â´xâ¥1æ¶ï¼g(x)åè°éå¢ï¼
â´g(x)ï¼g(1)â¥0
â´xâ¥1æ¶ï¼f(x)åè°éå¢ï¼
â´xâ(1ï¼+â)æ¶ï¼
f(x)ï¼f(1)=0
综ä¸ï¼aâ¤2
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