Target Exam

CUET

Subject

-- Mathematics - Section B1

Chapter

Indefinite Integration

Question:

Evaluate $\int \left\{ \frac{1}{\log x} - \frac{1}{(\log x)^2} \right\} dx$ (where $x > 1$).

Options:

$x \log x + C$

$\frac{\log x}{x} + C$

$\frac{x}{\log x} + C$

$x^2 \log x + C$

Correct Answer:

$\frac{x}{\log x} + C$

Explanation:

The correct answer is Option (3) → $\frac{x}{\log x} + C$

$\int \left\{ \frac{1}{\log x} - \frac{1}{(\log x)^2} \right\} dx$

$= \int \frac{1}{\log x} dx - \int \frac{1}{(\log x)^2} dx$

$= \frac{1}{\log x} \cdot \int 1 dx - \int \left\{ \frac{d}{dx} \left( \frac{1}{\log x} \right) \int 1 dx \right\} dx - \int \frac{1}{(\log x)^2} dx$

$= \frac{x}{\log x} + \int \frac{1}{(\log x)^2} \cdot \frac{1}{x} \cdot x dx - \int \frac{1}{(\log x)^2} dx$

$= \frac{x}{\log x} + \int \frac{1}{(\log x)^2} dx - \int \frac{1}{(\log x)^2} dx$

$= \frac{x}{\log x} + C$