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Math

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PROBLEM

If a=i+j+3k\mathbf{a}=\mathbf{i}+\mathbf{j}+3 \mathbf{k} and b=i+j+3k\mathbf{b}=\mathbf{i}+\mathbf{j}+3 \mathbf{k} Compute the cross product a×b\mathbf{a} \times \mathbf{b}.
a×b=i+j+k\mathbf{a} \times \mathbf{b}=\square \mathrm{i}+\square \mathrm{j}+\square \mathrm{k}

STEP 1

1. Vectors a\mathbf{a} and b\mathbf{b} are given in component form.
2. The cross product of two vectors results in a vector that is perpendicular to both.
3. The cross product of two identical vectors is the zero vector.

STEP 2

1. Identify the components of vectors a\mathbf{a} and b\mathbf{b}.
2. Use the formula for the cross product of two vectors.
3. Compute the cross product a×b\mathbf{a} \times \mathbf{b}.

STEP 3

Identify the components of vectors a\mathbf{a} and b\mathbf{b}:
a=i+j+3k\mathbf{a} = \mathbf{i} + \mathbf{j} + 3\mathbf{k} b=i+j+3k\mathbf{b} = \mathbf{i} + \mathbf{j} + 3\mathbf{k}

STEP 4

Recall the formula for the cross product of two vectors u=u1i+u2j+u3k\mathbf{u} = u_1 \mathbf{i} + u_2 \mathbf{j} + u_3 \mathbf{k} and v=v1i+v2j+v3k\mathbf{v} = v_1 \mathbf{i} + v_2 \mathbf{j} + v_3 \mathbf{k}:
u×v=(u2v3u3v2)i(u1v3u3v1)j+(u1v2u2v1)k\mathbf{u} \times \mathbf{v} = (u_2 v_3 - u_3 v_2) \mathbf{i} - (u_1 v_3 - u_3 v_1) \mathbf{j} + (u_1 v_2 - u_2 v_1) \mathbf{k}

SOLUTION

Apply the cross product formula to vectors a\mathbf{a} and b\mathbf{b}:
Since a=b\mathbf{a} = \mathbf{b}, the cross product a×b\mathbf{a} \times \mathbf{b} is:
a×b=(1331)i(1331)j+(1111)k\mathbf{a} \times \mathbf{b} = (1 \cdot 3 - 3 \cdot 1) \mathbf{i} - (1 \cdot 3 - 3 \cdot 1) \mathbf{j} + (1 \cdot 1 - 1 \cdot 1) \mathbf{k} Simplifying each term:
=(33)i(33)j+(11)k= (3 - 3) \mathbf{i} - (3 - 3) \mathbf{j} + (1 - 1) \mathbf{k} =0i+0j+0k= 0 \mathbf{i} + 0 \mathbf{j} + 0 \mathbf{k} The cross product a×b\mathbf{a} \times \mathbf{b} is:
0i+0j+0k\boxed{0 \mathbf{i} + 0 \mathbf{j} + 0 \mathbf{k}}

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