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Math Help - [SOLVED] Matrix Inverse

  1. #1
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    [SOLVED] Matrix Inverse

    Solve the system using the inverse of the coefficient matrix of the equivalent matrix equation

    2x+8y+6z=20
    4x+2y-2z=-2
    3x-y+z=11

    The answer is 2,-1,4

    Help!

    Thanks
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  2. #2
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    Quote Originally Posted by ToXic01 View Post
    Solve the system using the inverse of the coefficient matrix of the equivalent matrix equation

    2x+8y+6z=20
    4x+2y-2z=-2
    3x-y+z=11

    The answer is 2,-1,4

    Help!

    Thanks
    What have you tried? Where are you stuck? Have you reviewed similar examples in your class notes and textbook?
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  3. #3
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    similar examples skipped steps I still need help
    thanks
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  4. #4
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    Quote Originally Posted by ToXic01 View Post
    similar examples skipped steps I still need help

    thanks
    What steps do the examples in your notes apparently skip?

    AX = B \Rightarrow X = A^{-1}B.

    Now... please say exactly where you're stuck. Getting A? Finding A^{-1} ? Multiplying A^{-1}B ?
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  5. #5
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    1 0 0 0 -1/2 1
    0 1 0 1/14 5/7 -1
    0 0 1 1/14 -11/14 1
    the answer is not the same as the question
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  6. #6
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    Quote Originally Posted by ToXic01 View Post
    1 0 0 0 -1/2 1
    0 1 0 1/14 5/7 -1
    0 0 1 1/14 -11/14 1
    the answer is not the same as the question


    Apparently you mean that A^{-1}=\begin{pmatrix}0&\!\!\!-1\slash 2&1\\1\slash 14&5\slash 7&\!\!\!-1\\1\slash 14&\!\!\!-11\slash 14&1\end{pmatrix} . This is, of course, wrong...and I write "of course" because if you multiply this by A you do not get the

    identity matrix, so it shouldn't be a surprise that your answer doesn't match the actual one.

    You have the first column correct, but all the other entries are wrong, so...do it again, this time more carefully!

    Tonio
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  7. #7
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    i re-did it again and got the answer thanks
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