# maths test (revision)

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Hi I have a test on matrices in a couple of hours and was just wondering if there's anything I should watch out for or if you have some tips for remembering everything easily. Being a game programmer I have used matrices before and I did learn them at college a few years ago but I havn't done them for a while so tips please. I think it's just gonna be add, subtract, multiply and divide (also by scalers) and transpose etc and determinants. So shouldn't be to hard.

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Add, subtract is per-component. Multiply/divide by scalar is per-component. Vector it's 1xN or Nx1 matrix.

Multiply of matrices can be memorized using row by column rule - each output cell equal to dot product of row of first matrix and column of second. From there we can see that A*B != B*A in general, A*B=(B*A)T=BT*AT
where T stands for transpose.
Also we can see that number of columns in A must be equal to number of rows in B to make multiplication possible.

Divide, if defined at all, is multiply by inverse.
Determinant of 2x2 and 3x3 matrices can and must be memorized.
Inverse is best memorised using adjoints/determinants of submatrices (if you remember determinant). Also inverse of 3x3 matrix is related to cross product.
IIRC(but not completely sure,check on paper), 1st column of resulting matrix is equal to (1/determinant) *CrossProduct of 2nd and 3rd row, and so on.

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Cheers, got to go now though it's in 10 mins.

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OK. This thread is schoolwork/homework related, but it doesn't really totally violate forum policy, since JinJo didn't ask for the answer to a specific question (only advice).

Still, if you are unsure of the forum policy on schoolwork/homework, or didn't know there was such a policy, please review the Forum FAQ.

I'm closing the thread since JinJo seems to no longer need the advice.

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