For $x> 0$, the minimum value of $\frac{x}{\log_e x}$ is
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → $e$
Given: $x > 0$
Objective: Minimize the expression $\frac{x}{\log_e x}$
Let $f(x) = \frac{x}{\log_e x}$
Using calculus to find the minimum.
Let $f(x) = \frac{x}{\ln x}$
Differentiate using quotient rule:
$f'(x) = \frac{\ln x \cdot 1 - x \cdot \frac{1}{x}}{(\ln x)^2}$
$= \frac{\ln x - 1}{(\ln x)^2}$
Set $f'(x) = 0$:
$\ln x - 1 = 0$
$\ln x = 1$
$x = e$
Check the second derivative to confirm minimum:
$f''(x) = \frac{[(\ln x)^2 \cdot \frac{1}{x}] - [2(\ln x)(\ln x - 1) \cdot \frac{1}{x}]}{(\ln x)^4}$
At $x = e$, $\ln x = 1$
Denominator is positive, numerator becomes positive ⇒ $f''(x) > 0$
So, $x = e$ is a point of minimum.
Minimum value = $\frac{e}{\ln e} = \frac{e}{1} = e$