Question
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Choose the correct answer from the drop-down menu. Solve \( \sin 2 \theta=\cos \theta \) on the interval \( [0,2 \pi) \). \( \theta= \) Select... \( 0, \frac{\pi}{4}, \frac{\pi}{2} \), or \( \frac{3 \pi}{4} \)

Ask by Weston Chen. in the United Arab Emirates
Feb 26,2025

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Tutor-Verified Answer

Answer

The correct answer is \( \theta = \frac{\pi}{2} \).

Solution

To solve the equation sin 2θ = cos θ, start by rewriting sin 2θ using the double-angle formula:   sin 2θ = 2 sin θ cos θ So the equation becomes:   2 sin θ cos θ = cos θ This gives us two cases: Case 1: cos θ = 0   When cos θ = 0, the right-hand side is 0, and the equation holds if sin 2θ also equals 0. On the interval [0, 2π), cos θ = 0 when θ = π/2 and θ = 3π/2. Case 2: cos θ ≠ 0   If cos θ is not 0, we can divide both sides by cos θ:    2 sin θ = 1 ⟹ sin θ = 1/2   The solutions to sin θ = 1/2 on [0, 2π) are θ = π/6 and θ = 5π/6. So, the complete solution set is:   θ = π/6, 5π/6, π/2, 3π/2 However, since the drop-down menu provides only the choices 0, π/4, π/2, and 3π/4, the only value among our solutions that appears is π/2. Thus, the correct answer from the drop-down menu is:   θ = π/2

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To solve the equation \( \sin 2\theta = \cos \theta \), we can use the double angle identity for sine: \( \sin 2\theta = 2\sin \theta \cos \theta \). This turns our equation into \( 2 \sin \theta \cos \theta = \cos \theta \). If we factor out \( \cos \theta \), we get: \[ \cos \theta (2 \sin \theta - 1) = 0 \] This gives us two cases to solve: 1. \( \cos \theta = 0 \) 2. \( 2 \sin \theta - 1 = 0 \) or \( \sin \theta = \frac{1}{2} \) For the first case \( \cos \theta = 0 \), this happens at \( \theta = \frac{\pi}{2} \) within the interval \( [0, 2\pi) \). For the second case \( \sin \theta = \frac{1}{2} \), this occurs at \( \theta = \frac{\pi}{6}, \frac{5\pi}{6} \). However, since we need values that are among the options: - \( \theta = 0 \) - \( \theta = \frac{\pi}{4} \) - \( \theta = \frac{\pi}{2} \) - \( \theta = \frac{3\pi}{4} \) The correct answer is \( \theta = \frac{\pi}{2} \). Now, if you check through your answer choices, it seems like the down menu doesn't have a glaringly correct option listed based on traditional solutions. Perhaps you meant the larger scope of values in separate angles, but with your request, your answer is: \( \theta= \frac{\pi}{2} \).

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