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Math Help - Solve the system

  1. #1
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    Solve the system

    Solve the system by using elementary row operations on the equations. Follow the systematic elimination procedure.

    3x1 + 6x2 = 6
    4x1 + 7x2 = 11

    Ok so first I multiply each entry in row 1 by 1/3 to get 1 in the first column in row 1.

    Making it

    1 2 2
    4 7 11

    Then I multiply by -4 and add to get row 2 column 1 to = 0

    So

    1 2 2
    0 -1 3

    Then I multiply each entry in row 2 by -1 to make it positive

    there it's

    1 2 2
    0 1 -3

    Now I multiply each entry in row 2 by -2 and add it to row 1 to make column 2 in row 1 a 0.

    Now it's

    1 0 -4
    0 1 -3

    x1 = -4
    x2 = -3

    3(-4)+6(-3) = -30
    4(-4)+7(-3) = -37

    Where did I go wrong? >.<

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  2. #2
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    Re: Solve the system

    OK, before we continue, you always write down the ENTIRE system after each step, not just one side of it. All operations need to be done to both sides of each equation after all.
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  3. #3
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    Re: Solve the system

    I think I did that lol just looked over it again I'm getting the same answer?
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    Re: Solve the system

    Oops, I misread what you wrote, sorry. When you got to

    \displaystyle \begin{align*} \begin{matrix} 1 & 2 & \phantom{-}2 \\ 0 & 1 & -3  \end{matrix}  \end{align*}

    and multiplied each term in Row 2 by -2 and added to row 1, you should actually have gotten

    \displaystyle \begin{align*} \begin{matrix} 1 & 0 & \phantom{-}8 \\ 0 & 1 & -3 \end{matrix} \end{align*}
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  5. #5
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    Re: Solve the system

    Yeah I just got it lol I noticed it right after I left the site on my sheet I multiplied -2 by 3 which gave me -6 and messed up everything when indeed it was -2 * -3 :P, thanks though!

    3(8)+6(-3) =6
    4(8)+7(-3) = 11
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