MCQ
$\int\frac{\text{x}}{4+\text{x}^4}\text{ dx}$ is equal to:
  • A
    $\frac{1}{4}\tan^{-1}\text{x}^2+\text{C}$
  • $\frac{1}{4}\tan^{-1}\Big(\frac{\text{x}^2}{2}\Big)$
  • C
    $\frac{1}{2}\tan^{-1}\Big(\frac{\text{x}^2}{2}\Big)$
  • D
    none of these.

Answer

Correct option: B.
$\frac{1}{4}\tan^{-1}\Big(\frac{\text{x}^2}{2}\Big)$
$\text{I}=\int\frac{\text{x}}{4+\text{x}^4}\text{ dx}$
Put $\text{x}^2=\text{t}$
$2\text{xdx}=\text{dt}$
$\text{x dx}=\frac{\text{dt}}{2}$
$\text{I}=\int\frac{\frac{\text{dt}}{2}}{4+\text{t}^2}$
$\text{I}=\frac{1}{2}\tan^{-1}\Big(\frac{\text{t}}{2}\Big)+\text{C}$
$\text{I}=\frac{1}{2}\tan^{-1}\Big(\frac{\text{x}^2}{2}\Big)+\text{C}$

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