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Compute the dot product of the vectors \( \mathbf{u} \) and \( \mathbf{v} \), and find the angle between the vectors. \( \mathbf{u}=\langle-12,0,5\rangle \) and \( \mathbf{v}=\langle 1,2,3\rangle \). \( \mathbf{u} \cdot \mathbf{v}=3 \). (Type an integer or a simplified fraction.) Find the magnitude of the vectors. \( |\mathbf{u}|=13 \) and \( |\mathbf{v}|=\sqrt{14} \) (Type exact answers, using radicals as needed.) The angle between the vectors is \( \square^{\circ} \). (Type your answer in degrees. Do not round until the final answer. Then round to the nearest hundredth as needed.)

Ask by Griffiths Craig. in the United States
Feb 03,2025

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The dot product of vectors \( \mathbf{u} \) and \( \mathbf{v} \) is 3. The magnitudes of the vectors are \( |\mathbf{u}| = 13 \) and \( |\mathbf{v}| = \sqrt{14} \). The angle between the vectors is approximately \( 86.46^\circ \).

Solución

Let's compute the dot product, magnitudes of the vectors, and the angle between them step by step. ### Given Vectors: \[ \mathbf{u} = \langle -12, 0, 5 \rangle \quad \text{and} \quad \mathbf{v} = \langle 1, 2, 3 \rangle \] ### 1. Dot Product (\( \mathbf{u} \cdot \mathbf{v} \)) The dot product is calculated as: \[ \mathbf{u} \cdot \mathbf{v} = (-12)(1) + (0)(2) + (5)(3) = -12 + 0 + 15 = 3 \] \[ \mathbf{u} \cdot \mathbf{v} = \boxed{3} \] ### 2. Magnitudes of the Vectors - **Magnitude of \( \mathbf{u} \)**: \[ |\mathbf{u}| = \sqrt{(-12)^2 + 0^2 + 5^2} = \sqrt{144 + 0 + 25} = \sqrt{169} = 13 \] \[ |\mathbf{u}| = \boxed{13} \] - **Magnitude of \( \mathbf{v} \)**: \[ |\mathbf{v}| = \sqrt{1^2 + 2^2 + 3^2} = \sqrt{1 + 4 + 9} = \sqrt{14} \] \[ |\mathbf{v}| = \boxed{\sqrt{14}} \] ### 3. Angle Between the Vectors (\( \theta \)) The angle \( \theta \) between the vectors can be found using the dot product formula: \[ \mathbf{u} \cdot \mathbf{v} = |\mathbf{u}| \cdot |\mathbf{v}| \cdot \cos{\theta} \] Solving for \( \cos{\theta} \): \[ \cos{\theta} = \frac{\mathbf{u} \cdot \mathbf{v}}{|\mathbf{u}| \cdot |\mathbf{v}|} = \frac{3}{13 \cdot \sqrt{14}} \approx \frac{3}{48.6415} \approx 0.0617 \] Now, find \( \theta \) by taking the inverse cosine: \[ \theta = \arccos(0.0617) \approx 86.46^\circ \] \[ \theta = \boxed{86.46^\circ} \] ### Summary - **Dot Product**: \( \mathbf{u} \cdot \mathbf{v} = 3 \) - **Magnitudes**: - \( |\mathbf{u}| = 13 \) - \( |\mathbf{v}| = \sqrt{14} \) - **Angle Between Vectors**: \( 86.46^\circ \)

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To find the angle between the vectors \( \mathbf{u} \) and \( \mathbf{v} \), we use the formula for the dot product: \[ \mathbf{u} \cdot \mathbf{v} = |\mathbf{u}| |\mathbf{v}| \cos \theta \] Given: - \( \mathbf{u} \cdot \mathbf{v} = 3 \) - \( |\mathbf{u}| = 13 \) - \( |\mathbf{v}| = \sqrt{14} \) We can rearrange this formula to solve for \( \cos \theta \): \[ \cos \theta = \frac{\mathbf{u} \cdot \mathbf{v}}{|\mathbf{u}| |\mathbf{v}|} \] Plugging in the values: \[ \cos \theta = \frac{3}{13 \cdot \sqrt{14}} \] Calculating \( 13 \cdot \sqrt{14} \): \[ 13 \cdot \sqrt{14} = 13\sqrt{14} \] So we have: \[ \cos \theta = \frac{3}{13\sqrt{14}} \] To find \( \theta \), we take the inverse cosine: \[ \theta = \cos^{-1}\left(\frac{3}{13\sqrt{14}}\right) \] Now, let's calculate this using a calculator: 1. Calculate \( 13\sqrt{14} \) which is approximately \( 48.541 \). 2. Now, calculate \( \frac{3}{48.541} \) which is approximately \( 0.0618 \). 3. Finally, use the inverse cosine function: \[ \theta \approx \cos^{-1}(0.0618) \approx 85.44^{\circ} \] So the angle between the vectors is approximately: \[ \theta \approx 85.44^{\circ} \] Thus, rounding to the nearest hundredth: \[ \theta \approx 85.44^{\circ} \]

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