MCQ
If $f(x) = \sin x - {x \over 2}$ is increasing function, then
  • A
    $0 < x < {\pi \over 3}$
  • B
    $ - {\pi \over 3} < x < 0$
  • $ - {\pi \over 3} < x < {\pi \over 3}$
  • D
    $x = {\pi \over 2}$

Answer

Correct option: C.
$ - {\pi \over 3} < x < {\pi \over 3}$
c
(c) $f(x) = \sin x - \frac{x}{2} \Rightarrow f'(x) = \cos x - \frac{1}{2}$

$f'(x) > 0$ for increasing function

Obviously it is increasing for $ - \frac{\pi }{3} < x < \frac{\pi }{3}$.

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