Another problem:

Use matrix multiplication to find the projection of the vectors (3,4) (2,1) and (-3,2) during rotation for -30 deg. with center in the coordinate start (beginning).

tnx

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- May 5th 2011, 08:49 AMkaragorgeMatrix/projection of vectors problem
Another problem:

Use matrix multiplication to find the projection of the vectors (3,4) (2,1) and (-3,2) during rotation for -30 deg. with center in the coordinate start (beginning).

tnx - May 5th 2011, 10:30 AMHappyJoe
I don't see what your problem has to do with projections. Do you just want to find the images of the three vectors under a rotation of -30 degrees?

- May 5th 2011, 10:37 AMkaragorge
Yeah sorry bad translation - i meant the images of the three vectors.

- May 5th 2011, 10:52 AMHappyJoe
It should appear somewhere in your book or in your notes that the matrix that rotates a vector through an angle of v is

cos(v), -sin(v)

sin(v), cos(v).

You can apply this to your specific problem.

(LaTeX won't work for me at the moment.) - May 5th 2011, 11:09 AMkaragorge
Ok so it will look something like this:

1.

cos(-30) -sin(-30)

sin(-30) cos(-30)

and the matrix:

2.

3 2 -3

4 1 2

?

what should i do after - should i multiply 1. with 2.?

EDIT---

1.

-sqrt(3) / 2 , 1/2

-1/2 , -sqrt(3)/2 - May 5th 2011, 11:50 AMHappyJoe
The matrix in 1. rotates vectors -30 degrees, right. You don't need the matrix in 2. for anything.

The way the matrix rotates a vector is simply by multiplying the matrix with the vector, so to see where (-3,2) gets rotated, you multiply the matrix in 1. with the column vector

-3,

2,

in that order. - May 5th 2011, 11:53 AMkaragorge
tnx a lot for your help HappyJoe :)