MCQ
Let $f\left( x \right), x \in \left[ {0,\infty } \right)$ be a non-negative continuous function. If $f'\left( x \right)\cos x \le f\left( x \right)\sin x\ \forall\, x \ge 0$, then the value of $f(2\pi)$ is equal to
  • $0$
  • B
    $1$
  • C
    $\pi$
  • D
    None of these

Answer

Correct option: A.
$0$
a
$f^{\prime}(x) \cos x \leq f(x) \sin x$

$f^{\prime}(x) \cos x-f(x) \sin x \leq 0$

$(f(x) \cos x)^{\prime} \leq 0$

$\therefore $ $g(x)=f(x) \cos x$ is a monotonically nonincreasing function.

Since $\mathrm{f}(\mathrm{x})$ is non-negative, $\mathrm{f}(2 \pi)=0$

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