Q88 / 150 · MHT CET 2025 (22 Apr Shift 1) · Mathematics
For $N \in \mathbb{N}$,
$\frac{\mathrm{d}^{\mathrm{n}}}{\mathrm{~d} x^{\mathrm{n}}}(\log x)=$
- A$\frac{(n-1)!}{x^n}$
- B$\frac{\mathrm{n}!}{x^{\mathrm{n}}}$
- C$\frac{(\mathrm{n}-2)!}{x^{\mathrm{n}}}$
- Correct answerD$(-1)^{\mathrm{n}-1} \frac{(\mathrm{n}-1)!}{x^{\mathrm{n}}}$
Solution
Let $y = \log x$ and consider its $n$th derivative $\frac{d^n}{dx^n}(\log x)$.
The first derivative is $\frac{d}{dx}(\log x) = x^{-1}$.
Differentiating further reveals the pattern:
$\frac{d^2}{dx^2}(\log x) = -x^{-2}$
$\frac{d^3}{dx^3}(\log x) = 2x^{-3}$
$\frac{d^4}{dx^4}(\log x) = -6x^{-4}$
This establishes the general formula:
$\frac{d^n}{dx^n}(\log x) = (-1)^{n-1}\frac{(n-1)!}{x^n}$
Among the options, this corresponds to choice D.
Hence, the correct answer is option: 'D'.