The larger of $\cos (\log \theta)$ and $\log (\cos \theta)$, if $e^{-\pi / 2} < \theta < \pi / 2$ is

The larger of $\cos (\log \theta)$ and $\log (\cos \theta)$, if $e^{-\pi / 2} < \theta < \pi / 2$ is
  1. $\cos (\log \theta)$
  2. $\log (\cos \theta)$
  3. none of function is larger
  4. one of the two function is undefined on domain even to compare

Solution

$ \begin{aligned} & \text { } \cos (\log \theta), \theta \in\left(e^{\frac{-\pi}{2}}, \frac{\pi}{2}\right) \\ & e^{-\frac{\pi}{2}} < \theta < \frac{\pi}{2} \\ & \Rightarrow \quad-\frac{\pi}{2} < \log \theta < \log \frac{\pi}{2} \leq \frac{\pi}{2} \end{aligned} $ So, $\cos (\log \theta) \geq 0$ $ \log (\cos \theta) \leq 0 $ $ 0 \leq \cos \theta \leq 1 \text { in } \theta \in\left[e^{-\frac{\pi}{2}}, \frac{\pi}{2}\right] $ $ \therefore \quad \log (\cos \theta) \leq 0 $ Hence, $\cos (\log \theta) \geq \log (\cos \theta)$

Asked in: AP EAMCET 2021 (25 Aug Shift 1)

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