MCQ
$\int \frac{d x}{x\left(x^{2}+1\right)}$ बराबर है।
  • A
    -log |x| + $\frac{1}{2}$log(x2 + 1) + C
  • B
    log |x| + $\frac{1}{2}$ log (x2 + 1) + C
  • C
    $\frac{1}{2}$ log |x| + log (x2 + 1) + C
  • D
    log |x| - $\frac{1}{2}$log (x2 + 1) + C

Answer

माना $\frac{1}{x\left(x^{2}+1\right)}$ $=\frac{A}{x}+\frac{B x+C}{x^{2}+1}$
$\Rightarrow$ 1 = A(x2 + 1) + (Bx + C)x
दोनों पक्षों में x2, x तथा अचर राशि के गुणांकों को समान रखने पर,
A + B = 0, C = 0 तथा A = 1
इन समीकरणों को सरल करने पर,
A = 1, B = -1 और C = 0
$\therefore$ $\frac{1}{x\left(x^{2}+1\right)}$ $=\frac{1}{x}+\frac{-x}{x^{2}+1}$
$\therefore$ $\int \frac{1}{x\left(x^{2}+1\right)} d x$ $=\int\left(\frac{1}{x}-\frac{x}{x^{2}+1} d x\right)$
= log |x| - $\frac{1}{2}$log (x2 + 1) + C (माना x2 =  1 = t $\Rightarrow$ 2x dx = dt $\Rightarrow$ x dx = $\frac{dt}{2}$, $\therefore$ $\int$$\frac{x}{x^2 + 1}$dx = $\int$$\frac{1}{t}$$\frac{dt}{2}$ = $\frac{1}{2}$log t)

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