If $f(x) = \cos x,0 \le x \le {\pi \over 2}$, then the real number $ ‘c’ $ of the mean value theorem is

  • A

    ${\pi \over 6}$

  • B

    ${\pi \over 4}$

  • C

    ${\sin ^{ - 1}}\left( {{2 \over \pi }} \right)$

  • D

    ${\cos ^{ - 1}}\left( {{2 \over \pi }} \right)$

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Let $\psi_1:[0, \infty) \rightarrow R , \psi_2:[0, \infty) \rightarrow R , f:[0, \infty) \rightarrow R$ and $g :[0, \infty) \rightarrow R$ be functions such that

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and

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$(A)$ $f(\sqrt{\ln 3})+ g (\sqrt{\ln 3})=\frac{1}{3}$

$(B)$ For every $x>1$, there exists an $\alpha \in(1, x)$ such that $\psi_1(x)=1+\alpha x$

$(C)$ For every $x>0$, there exists a $\beta \in(0, x)$ such that $\psi_2(x)=2 x\left(\psi_1(\beta)-1\right)$

$(D)$ $f$ is an increasing function on the interval $\left[0, \frac{3}{2}\right]$

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$(B)$ $\psi_2(x) \leq 0$, for all $x>0$

$(C)$ $f( x ) \geq 1- e ^{- x ^2}-\frac{2}{3} x ^3+\frac{2}{5} x ^5$, for all $x \in\left(0, \frac{1}{2}\right)$

$(D)$ $g(x) \leq \frac{2}{3} x^3-\frac{2}{5} x^5+\frac{1}{7} x^7$, for all $x \in\left(0, \frac{1}{2}\right)$

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