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    hi, apparently the inverse for P is P^{-1} as shown,



    but i get

    \frac{1}{-3} [10, -5, -1][-13, 5, 1][-6,3,0]

    (with each square bracket being a row).

    can anyone tell me where i'm going wrong? thanks
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    Firstly, when you multiply P.P^-1 as given, do you get I?

    If so, then P^-1 must be right.

    If your inversion went wrong, then it's hard to see why without your working. I hate to invert matrices in public, because I make mistakes.
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    (Original post by ian.slater)
    Firstly, when you multiply P.P^-1 as given, do you get I?

    If so, then P^-1 must be right.

    If your inversion went wrong, then it's hard to see why without your working. I hate to invert matrices in public, because I make mistakes.
    i used this

    http://www.wikihow.com/Inverse-a-3X3-Matrix

    so M11 = (2x5)-(0x-1) = 10

    M12 = (1x5)-(0x0) = 5

    M13 = (1x-1)-(2x0) = -1

    until i got all three rows, then did the whole

    + - +
    - + -
    + - +

    thing, and multiplied it with the \frac{1}{det} = \frac{1}{-3}

    but none of my answers seem right!

    also i don't know what I should be, i use P^{-1}AP=D, if this has any connection?
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    At some stage you have to transpose the matrix of minors/cofactors. Your rows should be columns, so it looks like you haven't transposed.

    Does that sort it?
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    Also, when you say p^-1.A.P = D I think of diagonalising a matrix; eigenvectors and so on .. is that part of your question?
 
 
 
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