MCQ
Let $f(x) = \frac{x}{{1 + |x|}}$ be differentiable at  . . . .
  • $( - \infty ,\infty )$
  • B
    $[0,\infty ]$
  • C
    $( - \infty ,\,0) \cup (0,\infty )$
  • D
    $(0,\infty )$

Answer

Correct option: A.
$( - \infty ,\infty )$
a
$f(x)=\left\{\begin{array}{ll}{\frac{x}{1-x},} & {x<0} \\ {\frac{x}{1+x},} & {x \geq 0}\end{array}\right.$

$\Rightarrow f^{\prime}(x)=\left\{\begin{array}{ll}{\frac{x}{(1-x)^{2}},} & {x<0} \\ {\frac{x}{(1+x)^{2}}} & {x \geq 0}\end{array}\right.$

$\because f^{\prime}(x)$ exist at everywhere.

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