MCQ
The function $\text{f}(\text{x})=\cot^{-1}\text{x}+\text{x}$ increases in the interval:
  • A
    $(1,\infty)$
  • B
    $(-1,\infty)$
  • $(-\infty,\infty)$
  • D
    $(0,\infty)$

Answer

Correct option: C.
$(-\infty,\infty)$
$\text{f}(\text{x})=\cot^{-1}\text{x}+\text{x}$
$\text{f}'(\text{x})=\frac{-1}{1+\text{x}^2}+1$
$f(x)$ is increasing,
$\Rightarrow\frac{-1}{1+\text{x}^2}+1>0$
$\Rightarrow\frac{\text{x}^2}{1+\text{x}^2}>0$
Hence, $f(x)$ is increasing on $(-\infty,\infty).$

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