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Math Help - please help

  1. #1
    Junior Member
    Joined
    Feb 2009
    Posts
    49

    please help

    ok quick question.... why in system of equation is it the x y z are written in such a way across

    but in others the it is in written x
    y
    z
    vertically?
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  2. #2
    MHF Contributor

    Joined
    Apr 2005
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    1514
    Its pretty much convention but sometimes we want to distinguish between "row vectors" and "column vectors" because we want to treat them as matrices. We can multiply \begin{pmatrix}a & b & c\end{pmatrix}\begin{pmatrix}d \\ e\\ f\end{pmatrix} or \begin{pmatrix}a \\ b \\ c\end{pmatrix}\begin{pmatrix}d & e & f\end{pmatrix} but we cannot multiply \begin{pmatrix}a \\ b \\ c\end{pmatrix}\begin{pmatrix}d \\ e\\ f\end{pmatrix} or \begin{pmatrix}a & b & c\end{pmatrix}\begin{pmatrix}d & e & f\end{pmatrix}.

    To multiply matrices the number of columns of the first must equal the number of rows of the second. In the first example above those are both 3 and in the second example they are both 1. In the the third example, the number of columns in the first matrix is 1 and the number of rows in the second is 3. In the fourth example, the number of columens in the first matrix is 1 and the number of rows in the second is 1.
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