6. Application of derivatives — ગણિત ધોરણ 12 સાયન્સ — Question

$\therefore f'(x) = 2 - \frac{1}{{1 - {x^2}}} + \frac{1}{{\sqrt {1 + {x^2}} - x}}\left( {\frac{x}{{\sqrt {1 - {x^2}} }} - 1} \right)$

$ = \frac{{1 + 2{x^2}}}{{1 + {x^2}}} - \frac{1}{{\sqrt {1 + {x^2}} }} = \frac{{1 + 2{x^2}}}{{1 + {x^2}}} - \frac{{\sqrt {(1 + {x^2})} }}{{1 + {x^2}}}$

$ = \frac{{{x^2} + \sqrt {1 + {x^2}} (\sqrt {1 + {x^2}} - 1)}}{{1 + {x^2}}} \ge 0$ for all $x$

Hence $ f(x) $ is an increasing function on $( - \infty ,\,\infty )$ and

in particular on $[0,\;\infty )$.