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# Help! Thanks

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Let $$\mathbf{u}$$ and $$\mathbf{v}$$ be vectors such that $$\|\mathbf{u}\| = 3$$ and $$\|\mathbf{v}\| = 2,$$such that the angle between $$\mathbf{u}$$ and $$\mathbf{v}$$ when placed tail to tail is $$60^{\circ}$$. Let $$\mathbf{A}$$ be a matrix such that $$\mathbf{row}_1(\mathbf{A}) = \mathbf{u}, \mathbf{row}_2(\mathbf{A}) = \mathbf{v}.$$Then what are $$\mathbf{A} \mathbf{u}, \mathbf{A} \mathbf{v}$$ in that order? (Your answers should be numerical.)

Mar 23, 2023

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We know that the length of vector u is |u| = 3 and the length of vector v is |v| = 2. Also, the angle between u and v is 60 degrees. We can use this information to find the dot product of u and v, which will help us find their projections.

The dot product of u and v is given by:

u · v = |u| |v| cos θ

where θ is the angle between u and v. Substituting the values given in the problem, we get:

u · v = 3 × 2 × cos 60° = 3

Now, we can find the projection of u onto v using the formula:

projv(u) = (u · v / |v|) v

Substituting the values we know, we get:

projv(u) = (3/2) v

Similarly, we can find the projection of v onto u using the formula:

proju(v) = (v · u / |u|) u

Substituting the values we know, we get:

proju(v) = (3/2) u

Now, let's write the matrix A using the given rows:

A = [ u v ]

So, Au is the first row of A multiplied by u:

Au = (u · u, u · v)  = (9, 6)

And Av is the second row of A multiplied by v:

Av = (u · v, v · v) =  (6, 4)

Mar 23, 2023