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Thread: need help for simultaneous equation

  1. Aug 23rd 2009, 10:36 PM #1
    fvaras89
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    Unhappy need help for simultaneous equation

    the two equations are

    -2x -5y =21

    9x -7y = -65

    I have tried all methods and i keep getting different answers, could somebody help me?
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  2. Aug 23rd 2009, 10:48 PM #2
    red_dog
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    \left\{\begin{array}{ll}-2x-5y=21\\9x-7y=-65\end{array}\right.

    Multiply the first equation with 9 and the second with 2:

    \left\{\begin{array}{ll}-18x-45y=189\\18x-14y=-130\end{array}\right.

    Add the equations:

    -59y=59\Rightarrow y=-1

    Now plug y in any of the equations and find x.
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