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Math Help - Matrix

  1. #1
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    Matrix

    \begin{pmatrix} -1 & -2 \\9 & 4\end{pmatrix} \begin{pmatrix} 1-3k & -k \\9k & 3k+1\end{pmatrix}

    What does that equal? Thanks in advance.

    (EDIT: Sorry, I didn't realise that I was on Calculus forum hence posted incorrect thread. Thought I was in Urgent Homework Help forum.)
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  2. #2
    Moo
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    Hello !

    Quote Originally Posted by Air View Post
    \begin{pmatrix} -1 & -2 \\9 & 4\end{pmatrix} \begin{pmatrix} 1-3k & -k \\9k & 3k+1\end{pmatrix}

    What does that equal? Thanks in advance.

    (EDIT: Sorry, I didn't realise that I was on Calculus forum hence posted incorrect thread. Thought I was in Urgent Homework Help forum.)
    \begin{pmatrix} a&b \\ c&d \end{pmatrix} \begin{pmatrix} \alpha & \beta \\ \gamma & \delta \end{pmatrix}=\begin{pmatrix} a \alpha+b \gamma & a \beta+b \delta \\ c \alpha+d \gamma & c \beta+d \delta \end{pmatrix}
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  3. #3
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    Actually, it's like taking one row from the left matrix and multiply it with one column from the right matrix.


    (a \quad b)\begin{pmatrix} \alpha \\ \gamma \end{pmatrix} will give you the a_{11} element of the resulting matrix.

    (a \quad b) \begin{pmatrix} \beta \\ \delta \end{pmatrix} will give you the a_{12} element of the resulting matrix.


    For note :

    \begin{pmatrix} a_{11} & a_{12} \\ a_{21} & a_{22} \end{pmatrix}
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