Practicing Success

Target Exam

CUET

Subject

-- Mathematics - Section B1

Chapter

Applications of Derivatives

Question:

The function $f(x)=\frac{x}{\log x}$ increases on the interval

Options:

$(0, \infty)$

$(0, e)$

$(e, \infty)$

none of these

Correct Answer:

$(e, \infty)$

Explanation:

Clearly, f(x) is defined for x > 0

Now,

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

∴  $f'(x)>0 \Rightarrow \log x-1>0 \Rightarrow \log x>1 \Rightarrow x>e \Rightarrow x \in(e, \infty)$