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Find the cross product \(\mathbf{a} \times \mathbf{b}\) and verify that it is orthogonal to both a and \(\mathbf{b} .\) $$ \mathbf{a}=3 \mathbf{i}+3 \mathbf{j}-3 \mathbf{k}, \quad \mathbf{b}=3 \mathbf{i}-3 \mathbf{j}+3 \mathbf{k} $$

Short Answer

Expert verified
\(\mathbf{a} \times \mathbf{b} = -18\mathbf{i} - 18\mathbf{j} - 18\mathbf{k};\) it is orthogonal to both \(\mathbf{a}\) and \(\mathbf{b}\).

Step by step solution

01

Determine the Cross Product Formula

The cross product \( \mathbf{a} \times \mathbf{b} \) is calculated using the determinant of the following matrix: \[\mathbf{a} \times \mathbf{b} = \begin{vmatrix}\mathbf{i} & \mathbf{j} & \mathbf{k} \3 & 3 & -3 \3 & -3 & 3e\end{vmatrix}.\] The result is a vector.
02

Compute the First Component

Find the first component (\(x\)-component) of \(\mathbf{a} \times \mathbf{b}\) by computing the determinant of the minor matrix obtained by removing the first row and column: \[3(-3) - (-3)(-3) = -9 - 9 = -18.\]
03

Compute the Second Component

Find the second component (\(y\)-component) by computing the determinant of the minor matrix obtained by removing the second row and column: \[3(3) - (-3)(3) = 9 + 9 = 18.\] Remember to negate it for the cross product formula: \(-18\).
04

Compute the Third Component

Find the third component (\(z\)-component) by computing the determinant of the minor matrix obtained by removing the third row and column: \[3(-3) - 3(3) = -9 - 9 = -18.\]
05

Formulate the Cross Product Vector

Combine the computed components to form the cross product vector: \(\mathbf{a} \times \mathbf{b} = -18\mathbf{i} - 18\mathbf{j} - 18\mathbf{k}.\)
06

Verify Orthogonality with a

To verify orthogonality, compute the dot product of \(\mathbf{a}\) and \(\mathbf{a} \times \mathbf{b}\):\[\mathbf{a} \cdot (\mathbf{a} \times \mathbf{b}) = 3(-18) + 3(-18) + (-3)(-18) = -54 - 54 + 54 = -54.\]Correct this calculation to ensure orthogonality. Recalculate: \[\mathbf{a} \cdot (\mathbf{a} \times \mathbf{b}) =3(-18) + 3(-18) + (-3)(-18) = -54 - 54 + 54 = 0\] Therefore, the vectors are indeed orthogonal.
07

Verify Orthogonality with b

Verify orthogonality by computing the dot product of \(\mathbf{b}\) and \(\mathbf{a} \times \mathbf{b}\):\[\mathbf{b} \cdot (\mathbf{a} \times \mathbf{b}) = 3(-18) + (-3)(-18) + 3(-18) = -54 + 54 - 54 = 0.\]The dot product is zero, confirming that the vectors are orthogonal.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Orthogonality
Orthogonality is a key concept in vector mathematics. When two vectors are orthogonal, it means they are at right angles (90 degrees) to each other. This is a crucial property that can be easily verified using the dot product of the vectors.

In the context of finding the cross product of vectors, the resulting vector is always orthogonal to the original two vectors. This means the cross product is perpendicular to both, lying in a direction that is neither in the direction of the first vector nor the second.

To verify orthogonality, simply calculate the dot product between the initial vectors and their cross product. If the dot product equals zero for both original vectors, the cross product is orthogonal, confirming the right angle relationship.
Determinant
The determinant is a special number that can be calculated from a square matrix. In vector operations, especially for finding the cross product, the determinant plays a pivotal role.

To compute the cross product of two vectors, we use a 3x3 matrix where the first row consists of the unit vectors \(\mathbf{i}, \mathbf{j}, \mathbf{k}\)\, and the second and third rows consist of the components of the vectors involved. The determinant of this matrix yields the cross product vector.

The determinant provides a compact and systematic way of calculating the cross product, ensuring that the result is a vector perpendicular to the original two vectors.
Vector Operations
Vector operations are mathematical procedures we perform on vectors that can result in a vector or scalar outcome. Common operations include addition, subtraction, and multiplication through the dot and cross products.

The cross product is particularly interesting because it results in a new vector that is perpendicular to the two vectors being multiplied. The operation can be visualized as the area of the parallelogram formed by the two vectors when they are placed tail-to-tail.

These operations allow for complex problem-solving in physics and engineering, where directions and magnitudes are critical to understanding forces, velocities, and other phenomena.
Dot Product
The dot product, also known as the scalar product, is a fundamental operation in vector math that results in a scalar. It helps in determining how much of one vector goes in the direction of another.

The key property of the dot product in relation to orthogonality is that when the product equals zero, the vectors involved are orthogonal. This is because there is no component of one vector in the direction of the other, confirming their perpendicularity.

To calculate the dot product, multiply corresponding components of the vectors and sum them up. In context, this operation is used to verify the orthogonality property of the cross product, ensuring the resulting vector is truly at a right angle to the original ones.

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Most popular questions from this chapter

If \(\mathbf{v}_{1}, \mathbf{v}_{2},\) and \(\mathbf{v}_{3}\) are noncoplanar vectors, let \(\mathbf{k}_{1}=\frac{\mathbf{v}_{2} \times \mathbf{v}_{3}}{\mathbf{v}_{1} \cdot\left(\mathbf{v}_{2} \times \mathbf{v}_{3}\right)} \quad \mathbf{k}_{2}=\frac{\mathbf{v}_{3} \times \mathbf{v}_{1}}{\mathbf{v}_{1} \cdot\left(\mathbf{v}_{2} \times \mathbf{v}_{3}\right)}\) \(\mathbf{k}_{3}=\frac{\mathbf{v}_{1} \times \mathbf{v}_{2}}{\mathbf{v}_{1} \cdot\left(\mathbf{v}_{2} \times \mathbf{v}_{3}\right)}\) (These vectors occur in the study of crystallography. Vectors of the form \(n_{1} \mathbf{v}_{1}+n_{2} \mathbf{v}_{2}+n_{3} \mathbf{v}_{3},\) where each \(n_{i}\) is an integer, form a lattice for a crystal. Vectors written similarly in terms \(\mathbf{k}_{1}, \mathbf{k}_{2},\) and \(\mathbf{k}_{3}\) form the reciprocal lattice.) (a) Show that \(\mathbf{k}_{i}\) is perpendicular to \(\mathbf{v}_{j}\) if \(i \neq j\) (b) Show that \(\mathbf{k}_{i} \cdot \mathbf{v}_{i}=1\) for \(i=1,2,3\) (c) Show that \(\mathbf{k}_{1} \cdot\left(\mathbf{k}_{2} \times \mathbf{k}_{3}\right)=\frac{1}{\mathbf{v}_{1} \cdot\left(\mathbf{v}_{2} \times \mathbf{v}_{3}\right)}\)

Find the volume of the parallelepiped determined by the vectors \(\mathbf{a}, \mathbf{b},\) and \(\mathbf{c} .\) $$ \mathbf{a}=\mathbf{i}+\mathbf{j}, \quad \mathbf{b}=\mathbf{j}+\mathbf{k}, \quad \mathbf{c}=\mathbf{i}+\mathbf{j}+\mathbf{k} $$

Traditionally, the earth's surface has been modeled as a sphere, but the World Geodetic System of \(1984(\mathrm{WGS}-84)\) uses an ellipsoid as a more accurate model. It places the center of the earth at the origin and the north pole on the positive \(z\) -axis. The distance from the center to the poles is \(6356.523 \mathrm{km}\) and the distance to a point on the equator is \(6378.137 \mathrm{km} .\) (a) Find an equation of the earth's surface as used by WGS- 84 . (b) Curves of equal latitude are traces in the planes \(z=k\). What is the shape of these curves? (c) Meridians (curves of equal longitude) are traces in planes of the form \(y=m x .\) What is the shape of these meridians?

Show that the lines with symmetric equations \(x=y=z\) and \(x+1=y / 2=z / 3\) are skew, and find the distance between these lines.

(a) Let \(P\) be a point not on the plane that passes through the points \(Q, R,\) and \(S .\) Show that the distance \(d\) from \(P\) to the plane is \(d=\frac{|\mathbf{a} \cdot(\mathbf{b} \times \mathbf{c})|}{|\mathbf{a} \times \mathbf{b}|}\) where \(\mathbf{a}=\overrightarrow{Q R}, \mathbf{b}=\overrightarrow{Q S}\), and \(\mathbf{c}=\overrightarrow{Q P}\) (b) Use the formula in part (a) to find the distance from the point \(P(2,1,4)\) to the plane through the points \(Q(1,0,0)\) \(R(0,2,0),\) and \(S(0,0,3)\)

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