MCQ
$\int \frac{1}{x \sqrt{x^4-1}} d x=?$
  • A
    $\operatorname{cosec}^{-1} x^2+C$
  • $\frac{1}{2} \sec ^{-1} x^2+C$
  • C
    $\sec ^{-1} x^2+C$
  • D
    $2 \operatorname{cosec}^{-1} x^2+C$

Answer

Correct option: B.
$\frac{1}{2} \sec ^{-1} x^2+C$
Formula $:- \int x^n d x=\frac{x^{n+1}}{n+1}+c ; \int \frac{1}{t \sqrt{t^2-1}} d t=\sec ^{-1} t+c$
Therefore,
 Put $x^2=t$
$\Rightarrow 2 xdx=dt$
$=\int \frac{1}{x \sqrt{t^2-1}} \times \frac{d t}{2 x} \Rightarrow \frac{1}{2} \int \frac{1}{t \sqrt{t^2-1}} d t$
$=\frac{1}{2} \sec ^{-1} t+c$
$=\frac{1}{2} \sec ^{-1} x^2+c$

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