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Math Help - [Matrices Inverses] Finding the inverse equality to I doesn't work

  1. #1
    Junior Member Cthul's Avatar
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    [Matrices Inverses] Finding the inverse equality to I doesn't work

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  2. #2
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    Hello, Cthul!

    I don't understand your title.
    What doesn't work?


    Find the inverse of: . \begin{bmatrix}\text{-}2&\text{-}7 \\ 1&4\end{bmatrix}

    . . (A)\;\begin{bmatrix}4&7\\ \text{-}1&\text{-}2\end{bmatrix}\qquad (B)\;\begin{bmatrix}\text{-}2&1\\7&\text{-}4\end{bmatrix} \qquad (C)\;\begin{bmatrix}\text{-}4&\text{-}7 \\ 1 & 2 \end{bmatrix} . . (D)\;\begin{bmatrix}1 & \text{-}7 \\ 2&\text{-}4\end{bmatrix}\qquad (E)\;\begin{bmatrix}\text{-}1 & 2 \\ 4&\text{-}7\end{bmatrix}

    Answer (C) works . . . check it out!

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  3. #3
    Junior Member Cthul's Avatar
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    It makes \begin{bmatrix}1&0 \\ 0&1\end{bmatrix}
    I tried finding an inverse.
    I got:
    \frac{1}{15}\begin{bmatrix}4&1 \\ \text{-}7&\text{-}2\end{bmatrix} \begin{bmatrix}1&0 \\ 0&1\end{bmatrix}=A
    How'd you find it works for C?

    EDIT: I see what I did wrong now, nevermind. I know how to do it now.
    Last edited by Cthul; June 1st 2010 at 09:41 PM.
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