Q93 / 150 · MHT CET 2025 (19 Apr Shift 2) · Mathematics
$\int \frac{x d x}{(x-1)(x-2)}=$
- A$\log \left(\frac{x-1}{x-2}\right)+c$, where $c$ is the constant of integration
- B$\log \left(\frac{x-2}{(x-1)^2}\right)+c$, where $c$ is the constant of integration
- C$\log \left(\frac{x-2}{x-1}\right)+c$, where $c$ is the constant of integration
- Correct answerD$\log \left(\frac{(x-2)^2}{x-1}\right)+c$, where $c$ is the constant of integration
Solution
Decompose the integrand using partial fractions:
$\frac{x}{(x-1)(x-2)} = \frac{A}{x-1} + \frac{B}{x-2}$
Clearing denominators yields $x = A(x-2) + B(x-1)$.
At $x = 1$: $1 = A(-1)$, so $A = -1$.
At $x = 2$: $2 = B(1)$, so $B = 2$.
The decomposition becomes $\frac{-1}{x-1} + \frac{2}{x-2}$.
Integrating term by term:
$-\int \frac{1}{x-1}\,dx + 2\int \frac{1}{x-2}\,dx = -\ln|x-1| + 2\ln|x-2| + C$
Applying logarithmic identities:
$\ln|(x-2)^2| - \ln|x-1| + C = \ln\left|\frac{(x-2)^2}{x-1}\right| + C$
This expression corresponds to option D.
Final answer: $\boxed{D}$
Hence, the correct answer is option: 'D'.