题(2)当(xin (1,+infty))时,求证:(dfrac{ ext{e}(x-1)}{ ext{e}^x}<ln x<x^2-x).
(ding{192})函数(y=dfrac{ln x}{x})在(x=1)处切线放缩(Rightarrow dfrac{ln x}{x}leqslant x-1)
(Rightarrow ln x<x^2-x)(其中(x>1))
(ding{193})函数(y=x ln x)在(x=1)处切线放缩(Rightarrow xln xgeqslant x-1)
(Rightarrow ln x>dfrac{x-1}{x}>dfrac{ ext{e}(x-1)}{ ext{e}^x})(其中(x>1))
其中函数(y= ext{e}^x)在(x=1)处切线放缩(Rightarrow ext{e}^xgeqslant ext{e}xRightarrow) 当(x>1)时( ext{e}^x> ext{e}x)