1)

The minimum value of $\frac{x}{\log x}$ is


A) e

B) $\frac{1}{e}$

C) $e^{2}$

D) $e^{3}$

Answer:

Option A

Explanation:

 Let  f(x)= $\frac{x}{\log x}$

 $\Rightarrow$    $f'(x)=\frac{\log x-1}{(\log x)^{2}}$

 For maxima  and minima , put f'(x)=0

 $\log x-1=0$

 $\Rightarrow$   $x=e$

 Now, f"(x)

    =  $\frac{(\log x)^{2}.\frac{1}{x}-(\log x-1).\frac{2 \log x}{x}}{(\log x)^{4}}$

  $\Rightarrow$     $f"(e)=\frac{\frac{1}{e}-0}{1}=\frac{1}{e} >0$

 $\therefore$   f(x)  is minimum  at x=e

Hence, minimum value of f(x) at x=e is 

    $f(e) =\frac{e}{\log e}=e$