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Say I have a square represented by the following matrix:

0   0
10  0
10  10
0   10
0   0

Now, what would I multiply this matrix by to rotate the square (or what ever shape it is) around its center point x degrees?

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Actually, a simple matrix multiplication won't do. One thing you can do is find the center of that square, translate all your coordinates so that the center is at the origin, apply a rotation matrix (mind the sign of your angles!), and then undo the translation you previously did. – J. M. Oct 17 '11 at 0:48
A more precise way to state the above might be 'Say I have a square represented by the following vectors', because I don't think you mean the numbers above to represent a matrix. It looks like you are listing 5 (well, 4) vectors, -each- of which you can multiply by a rotation matrix, but not all at once. – Rex Butler Oct 17 '11 at 1:59

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