Question
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Drag and drop the correct answer into the space(s) provided. If \( \tan \theta=\frac{1}{2} \) on the interval \( \left(\pi, \frac{3 \pi}{2}\right) \), find \( \sin 2 \theta, \cos 2 \theta \), and \( \tan 2 \theta \). \( \sin \theta=-\frac{\sqrt{5}}{5} \) and \( \cos \theta=-\frac{2 \sqrt{5}}{5} \) \( \sin 2 \theta= \) \( \cos 2 \theta= \) \( \tan 2 \theta= \) \( -\frac{\sqrt{5}}{2} \)

Ask by Pearson Bowman. in the United Arab Emirates
Feb 26,2025

Upstudy AI Solution

Tutor-Verified Answer

Answer

sin 2θ = 4/5 cos 2θ = 3/5 tan 2θ = 4/3

Solution

We are given that   tan θ = 1/2   with θ in (π, 3π/2), and that   sin θ = –(√5)/5   cos θ = –(2√5)/5. Step 1. Verify tan θ:   tan θ = sin θ/cos θ = [–(√5)/5] / [–(2√5)/5] = 1/2, which confirms the given value. Step 2. Find sin 2θ using the double-angle formula:   sin 2θ = 2 sin θ cos θ. Plug in the values:   sin 2θ = 2 [–(√5)/5][–(2√5)/5] = 2 (2·5/25) = 2 (10/25) = 20/25 = 4/5. Step 3. Find cos 2θ using the formula:   cos 2θ = cos²θ – sin²θ. Compute:   cos²θ = [–(2√5)/5]² = 4·5/25 = 20/25,   sin²θ = [–(√5)/5]² = 5/25. Then,   cos 2θ = 20/25 – 5/25 = 15/25 = 3/5. Step 4. Find tan 2θ using:   tan 2θ = sin 2θ / cos 2θ = (4/5) / (3/5) = 4/3. Thus, the answers to drag and drop are:   sin 2θ = 4/5   cos 2θ = 3/5   tan 2θ = 4/3 (Note: The candidate answer “–√5/2” is not used in these answers.)

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Bonus Knowledge

When we have \( \tan \theta = \frac{1}{2} \), that means for some angle \( \theta \), the sine and cosine must follow that ratio. Since \( \theta \) is in the third quadrant, both sine and cosine are negative. You already have \( \sin \theta = -\frac{\sqrt{5}}{5} \) and \( \cos \theta = -\frac{2\sqrt{5}}{5} \). To find \( \sin 2\theta \), we can use the identity: \[ \sin 2\theta = 2 \sin \theta \cos \theta \] Plugging in the values: \[ \sin 2\theta = 2 \left(-\frac{\sqrt{5}}{5}\right)\left(-\frac{2\sqrt{5}}{5}\right) = 2 \cdot \frac{2 \cdot 5}{25} = \frac{20}{25} = \frac{4}{5} \] Next, for \( \cos 2\theta \): \[ \cos 2\theta = \cos^2 \theta - \sin^2 \theta \] Calculating individually, \[ \cos^2 \theta = \left(-\frac{2\sqrt{5}}{5}\right)^2 = \frac{4 \cdot 5}{25} = \frac{20}{25} = \frac{4}{5} \] \[ \sin^2 \theta = \left(-\frac{\sqrt{5}}{5}\right)^2 = \frac{5}{25} = \frac{1}{5} \] Now plug those into the formula: \[ \cos 2\theta = \frac{4}{5} - \frac{1}{5} = \frac{3}{5} \] Lastly, for \( \tan 2\theta \): \[ \tan 2\theta = \frac{\sin 2\theta}{\cos 2\theta} \] So we calculate: \[ \tan 2\theta = \frac{\frac{4}{5}}{\frac{3}{5}} = \frac{4}{3} \] Putting it all together: \[ \sin 2 \theta = \frac{4}{5} \] \[ \cos 2 \theta = \frac{3}{5} \] \[ \tan 2 \theta = \frac{4}{3} \]

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