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Math Help - Matrices

  1. #1
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    Matrices

    here I put my answer as a picture









    Last edited by mr fantastic; April 9th 2010 at 12:07 AM. Reason: Changed post title
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  2. #2
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    Quote Originally Posted by r-soy View Post
    here I put my answer as a picture









    Dear r-soy,

    1) A^{-1}=\left(\begin{array}{ccc}-1&1&1\\-2&3&2\\0.5&-0.25&-0.25\end{array}\right)

    2) A) x_{1}=-1~and~x_{2}=3

    B) x_{1}=1~and~x_{2}=2

    Hope this will help you.
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  3. #3
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    Quote Originally Posted by Sudharaka View Post
    Dear r-soy,

    1) A^{-1}=\left(\begin{array}{ccc}-1&1&1\\-2&3&2\\0.5&-0.25&-0.25\end{array}\right)

    2) A) x_{1}=-1~and~x_{2}=3

    B) x_{1}=1~and~x_{2}=2

    Hope this will help you.
    But I wrote same answer which you wrote here

    ?????????????????????

    where my mistake
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  4. #4
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    Quote Originally Posted by r-soy View Post
    But I wrote same answer which you wrote here

    ?????????????????????

    where my mistake
    Dear r-soy,

    I solved these problems myself and wrote down only the answers. If they tally with your answers that means you have done these problems correctly. Congratulations!!
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  5. #5
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    Quote Originally Posted by Sudharaka View Post
    Dear r-soy,

    I solved these problems myself and wrote down only the answers. If they tally with your answers that means you have done these problems correctly. Congratulations!!

    see In Q1 Is the check is true or not ?

    and also any mistake in Q1
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  6. #6
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    Quote Originally Posted by r-soy View Post
    see In Q1 Is the check is true or not ?

    and also any mistake in Q1
    Dear r-soy,

    I really don't understand what you mean?? If you think that there is a mistake in Q1, my answer is "NO".
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  7. #7
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    but some teacher said You have obviously made a mistake somewhere, either in the inverse or in your check. When you multiplied A-1 by A, you should have gotten the identity matrix I, but you didn't. That should be a clue that you've done something wrong.


    please hlep me
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  8. #8
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    Quote Originally Posted by r-soy View Post
    but some teacher said You have obviously made a mistake somewhere, either in the inverse or in your check. When you multiplied A-1 by A, you should have gotten the identity matrix I, but you didn't. That should be a clue that you've done something wrong.


    please hlep me
    Dear r-soy,

    Yes. You have done something wrong in getting the inverse of A. Your answer is not exactly mine.

    My answer: A^{-1}=\left(\begin{array}{ccc}-1&1&1\\-2&3&2\\0.5&-0.25&-0.25\end{array}\right)

    Your answer: A^{-1}=\left(\begin{array}{ccc}-1&1&1\\-2&3&2\\0.5&{\color{red}0.25}&-0.25\end{array}\right)
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  9. #9
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    that means there is a mistake on the my checking ? ? ? ? ? ? ? ?
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  10. #10
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    Quote Originally Posted by r-soy View Post
    that means there is a mistake on the my checking ? ? ? ? ? ? ? ?
    Dear r-soy,

    Ah!! I found your mistake,

    Please recheck, the line...

    co-factor matrix= \left(\begin{array}{ccc}(4-0)&-(-8-0)&(2-4)\\-(0+4)&(4-16)&{\color{red}-(0+1)}\\(0-4)&-(0+8)&(1-0)\end{array}\right)

    Does this solve your problem??
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  11. #11
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    I try to correct my answer

    help me if true now or not >>



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  12. #12
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    Quote Originally Posted by r-soy View Post
    I try to correct my answer

    help me if true now or not >>



    Dear r-soy,

    Your "check" is wrong. You should get the identitiy matrix. Go through your matrix multiplication again.
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  13. #13
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    my dear i try but i get same the answer

    please help me >>
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  14. #14
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    Quote Originally Posted by r-soy View Post
    my dear i try but i get same the answer

    please help me >>
    Dear r-soy,

    Please check the highlighted parts...

    \left(\begin{array}{ccc}-1&1&1\\-2&3&2\\{\frac{2}{4}}&{-\frac{1}{4}}&{-\frac{1}{4}}\end{array}\right)\left(\begin{array}{  ccc}1&0&4\\-2&1&0\\4&-1&4\end{array}\right)=\left(\begin{array}{ccc}1&0&  0\\0&1&0\\{\color{red}-1}&{\color{red}-\frac{2}{4}}&1\end{array}\right)
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