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 answer
    D
    $\log \left(\frac{(x-2)^2}{x-1}\right)+c$, 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'.

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