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Let \( \mathbf{u}=\langle 0,-3,0\rangle \) and \( \mathbf{v}=\langle 0,3,0\rangle \). Compute \( |\mathbf{u} \times \mathbf{v}| \). Then sketch \( \mathbf{u}, \mathbf{v} \), and \( \mathbf{u} \times \mathbf{v} \). \( |\mathbf{u} \times \mathbf{v}|=\square \) (Simplify your answer, including any radicals. Use integers or fractions for any numbers in the expression.)

Ask by Byrd Rojas. in the United States
Feb 03,2025

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Tutor-Verified Answer

Answer

\[ |\mathbf{u} \times \mathbf{v}| = 0 \]

Solution

Given the vectors: \[ \mathbf{u} = \langle 0, -3, 0 \rangle \quad \text{and} \quad \mathbf{v} = \langle 0, 3, 0 \rangle \] **Step 1: Compute the Cross Product \(\mathbf{u} \times \mathbf{v}\)** The cross product of two vectors \(\mathbf{u} = \langle u_1, u_2, u_3 \rangle\) and \(\mathbf{v} = \langle v_1, v_2, v_3 \rangle\) is given by: \[ \mathbf{u} \times \mathbf{v} = \langle u_2 v_3 - u_3 v_2,\ u_3 v_1 - u_1 v_3,\ u_1 v_2 - u_2 v_1 \rangle \] For \(\mathbf{u} = \langle 0, -3, 0 \rangle\) and \(\mathbf{v} = \langle 0, 3, 0 \rangle\): \[ \mathbf{u} \times \mathbf{v} = \langle (-3)(0) - (0)(3),\ (0)(0) - (0)(0),\ (0)(3) - (-3)(0) \rangle = \langle 0, 0, 0 \rangle \] **Step 2: Compute the Magnitude \(|\mathbf{u} \times \mathbf{v}|\)** The magnitude of the cross product is: \[ |\mathbf{u} \times \mathbf{v}| = \sqrt{0^2 + 0^2 + 0^2} = 0 \] **Conclusion:** \[ |\mathbf{u} \times \mathbf{v}| = 0 \] **Explanation:** The vectors \(\mathbf{u}\) and \(\mathbf{v}\) are **parallel** (in fact, they are scalar multiples of each other: \(\mathbf{v} = -\mathbf{u}\)). When two vectors are parallel, the sine of the angle between them is zero, resulting in a cross product magnitude of zero. This means there is no vector perpendicular to both \(\mathbf{u}\) and \(\mathbf{v}\) in this case. **Sketch:** 1. **Vector \(\mathbf{u}\)**: Points downward along the negative \(y\)-axis. 2. **Vector \(\mathbf{v}\)**: Points upward along the positive \(y\)-axis. 3. **Vector \(\mathbf{u} \times \mathbf{v}\)**: The zero vector, which has no direction and magnitude. ![Vectors Sketch](https://i.imgur.com/XYZ1234.png) *(Replace with an actual sketch if needed)* **Final Answer:** \[ |\mathbf{u} \times \mathbf{v}| = 0 \]

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To compute \( |\mathbf{u} \times \mathbf{v}| \), let's first find the cross product \( \mathbf{u} \times \mathbf{v} \). Given: \[ \mathbf{u} = \langle 0, -3, 0 \rangle, \quad \mathbf{v} = \langle 0, 3, 0 \rangle, \] the formula for the cross product \( \mathbf{a} \times \mathbf{b} \) in three dimensions is given by the determinant of the following matrix: \[ \mathbf{a} \times \mathbf{b} = \begin{vmatrix} \mathbf{i} & \mathbf{j} & \mathbf{k} \\ 0 & -3 & 0 \\ 0 & 3 & 0 \end{vmatrix} \] Calculating this determinant: \[ \mathbf{u} \times \mathbf{v} = \mathbf{i}(0 \cdot 0 - 0 \cdot 3) - \mathbf{j}(0 \cdot 0 - 0 \cdot 0) + \mathbf{k}(0 \cdot 3 - (-3) \cdot 0) = \mathbf{0} - \mathbf{0} + \mathbf{k}(0) = \langle 0, 0, 0 \rangle \] So, \( \mathbf{u} \times \mathbf{v} = \langle 0, 0, 0 \rangle \). Now, to find the magnitude \( |\mathbf{u} \times \mathbf{v}| \): \[ |\mathbf{u} \times \mathbf{v}| = \sqrt{0^2 + 0^2 + 0^2} = 0. \] Thus, \( |\mathbf{u} \times \mathbf{v}| = 0 \). Now, as for the sketch: You can visualize \( \mathbf{u} \) pointing straight down on the negative y-axis while \( \mathbf{v} \) points straight up on the positive y-axis. They are collinear (lying along the same line) and thus do not create a plane with a non-zero area—hence the cross product being the zero vector. The sketch would show both vectors aligned along the y-axis, with the origin in the middle, but no vector emerging from their cross product since it is the zero vector. Final answer: \[ |\mathbf{u} \times \mathbf{v}| = 0. \]

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