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Identify the correct options :...

Identify the correct options :

A

` (sin 3 alpha )/(cos 2 alpha) gt 0 ` for ` alpha in ((3 pi)/(8), (23 pi)/(48))`

B

` (sin 3 alpha )/(cos 2 alpha) lt 0 ` for ` alpha in ((13 pi)/(48), (14 pi)/(48))`

C

` (sin 2 alpha )/(cos alpha) lt 0 ` for ` alpha in (-(pi)/(2), 0)`

D

` (sin 2 alpha )/(cos alpha) gt 0 ` for ` alpha in ((13 pi)/(48), (14 pi)/(48))`

Text Solution

AI Generated Solution

The correct Answer is:
To solve the problem, we need to analyze the expression \(\frac{\sin 3\alpha}{\cos 2\alpha}\) and determine the conditions under which it is greater than zero. ### Step-by-Step Solution: 1. **Understanding the Expression**: We start with the expression: \[ \frac{\sin 3\alpha}{\cos 2\alpha} > 0 \] This implies that both \(\sin 3\alpha\) and \(\cos 2\alpha\) must either be both positive or both negative. 2. **Finding Conditions for \(\sin 3\alpha > 0\)**: The sine function is positive in the intervals: \[ 3\alpha \in (0, \pi) \cup (2\pi, 3\pi) \cup (4\pi, 5\pi) \ldots \] This translates to: \[ \alpha \in \left(0, \frac{\pi}{3}\right) \cup \left(\frac{2\pi}{3}, \pi\right) \cup \left(\frac{4\pi}{3}, \frac{5\pi}{3}\right) \ldots \] 3. **Finding Conditions for \(\cos 2\alpha > 0\)**: The cosine function is positive in the intervals: \[ 2\alpha \in (-\frac{\pi}{2}, \frac{\pi}{2}) \cup \left(\frac{3\pi}{2}, \frac{5\pi}{2}\right) \ldots \] This translates to: \[ \alpha \in \left(-\frac{\pi}{4}, \frac{\pi}{4}\right) \cup \left(\frac{3\pi}{4}, \frac{5\pi}{4}\right) \ldots \] 4. **Combining the Conditions**: We need to find the intersection of the intervals where both conditions hold true: - From \(\sin 3\alpha > 0\): \(\alpha \in (0, \frac{\pi}{3})\) or \((\frac{2\pi}{3}, \pi)\) - From \(\cos 2\alpha > 0\): \(\alpha \in (-\frac{\pi}{4}, \frac{\pi}{4})\) or \((\frac{3\pi}{4}, \frac{5\pi}{4})\) The only overlapping interval is: \[ \alpha \in (0, \frac{\pi}{4}) \] 5. **Analyzing the Negative Cases**: Now we consider when both \(\sin 3\alpha < 0\) and \(\cos 2\alpha < 0\): - \(\sin 3\alpha < 0\) gives us intervals like \((\frac{\pi}{3}, \pi)\) and so on. - \(\cos 2\alpha < 0\) gives us intervals like \((\frac{\pi}{4}, \frac{3\pi}{4})\). The overlapping interval here is: \[ \alpha \in \left(\frac{\pi}{3}, \frac{3\pi}{4}\right) \] 6. **Final Intervals**: Thus, the complete solution for \(\frac{\sin 3\alpha}{\cos 2\alpha} > 0\) is: \[ \alpha \in (0, \frac{\pi}{4}) \cup \left(\frac{\pi}{3}, \frac{3\pi}{4}\right) \] ### Conclusion: Based on the intervals derived, we can now check the provided options to identify which ones fall within these ranges.
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