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Math Help - Matrix calculation/algebra!

  1. #1
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    Matrix calculation/algebra!

    X is a 3x3 matrix (spaces used for separation)

    1 3 9
    1 4 16
    1 5 25

    I want to know X( X - 12I) where I is the 3x3 identity matrix. Can someone explain/show?
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  2. #2
    MHF Contributor
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    Quote Originally Posted by acu04385 View Post
    X is a 3x3 matrix (spaces used for separation)

    1 3 9
    1 4 16
    1 5 25

    I want to know X( X - 12I) where I is the 3x3 identity matrix. Can someone explain/show?
    As it is written, it says multiple the identity matrix by 12, subtract X from the 12I and then multiple X by the that matrix.

    \begin{bmatrix}<br />
1 & 3 & 9\\ <br />
1 & 4 & 16\\ <br />
1 & 5 & 25<br />
\end{bmatrix}*\bigg(\begin{bmatrix}<br />
1 & 3 & 9\\ <br />
1 & 4 & 16\\ <br />
1 & 5 & 25<br />
\end{bmatrix}-\begin{bmatrix}<br />
12 & 0 & 0\\ <br />
0 & 12 & 0\\ <br />
0 & 0 & 12<br />
\end{bmatrix}\bigg)
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  3. #3
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    Thumbs up thanks!

    Many thanks i was confusing myself with the relationship IA = AI = A
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