MCQ
If $f(t) = \int_{\, - t}^{\,t} {\frac{{dx}}{{1 + {x^2}}},} $ then $f'(1)$ is
  • A
    $Zero$
  • B
    $2/3$
  • C
    $ - \,1$
  • $1$

Answer

Correct option: D.
$1$
d
(d) Given $f(t) = \int_{ - t}^t {\frac{{dx}}{{1 + {x^2}}}} $

$ = [{\tan ^{ - 1}}x]_{ - t}^t$

$ = 2{\tan ^{ - 1}}t$

Differentiating with respect to $t$,

$f'(t) = \frac{2}{{1 + {t^2}}}$

==> $f'(1) = \frac{2}{2} = 1$.

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