MCQ
The range of function $f (x)=\log _{ e } \sqrt{4-x^2}$ is given by
  • A
    $(0, \infty)$
  • B
    $(-\infty, \infty)$
  • $\left(-\infty, \log _e 2\right]$
  • D
    $\left(\log _e 2, \infty\right)$

Answer

Correct option: C.
$\left(-\infty, \log _e 2\right]$
(C)
Let $y=\log _e \sqrt{4-x^2} \Rightarrow e ^y=\sqrt{4-x^2}$
$\Rightarrow e ^{2 y}=4-x^2 \Rightarrow x^2=4- e ^{2 y} \Rightarrow x=\sqrt{4- e ^{2 y}}$
$\therefore 4-e^{2 y} \geq 0$
$\Rightarrow e ^{2 y} \leq 4 \Rightarrow 2 y \leq \log _{ e } 4$
$\Rightarrow y \leq \frac{1}{2} \log _{ e } 4 \Rightarrow y \leq \log _{ e } 2$
$\therefore y \in\left(-\infty, \log _e 2\right]$

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