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    Sharpe's Avatar
    Sharpe Posts: 8, Reputation: 1
    New Member
     
    #1

    Jul 5, 2007, 07:18 PM
    System of equations
    7 x + 4 y = - 2,
    10 x - 3 y = 32
    I need help with this question.
    I am using elimination.
    I keep get x=2 but I can't find y.
    So I'm guessing that x might be wrong..
    But I don't know what I'm doing wrong:confused:
    BIsovski's Avatar
    BIsovski Posts: 2, Reputation: 1
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    #2

    Jul 5, 2007, 07:58 PM
    Okay,

    There are many ways to solve system equations, or in this case so called 2 equations with 2 unknowns.

    Below I provide one method, but I encourage you to find your own method

    Looking at your problem:

    7 x + 4 y = - 2,
    10 x - 3 y = 32

    We want to eliminate one unknown and solve for the other.
    The common denomitor of 4y and (-) 3y is 12. If we multiply the first equation with 3 we get 12y an the second equation with 4 we get (-) 12y, therefore

    (3) 7x + (3) 4y = (3) (-2)
    (4) 10x - (4) 3y = (4) 32

    from here we get

    21x +12y = -6
    40x -12y = 128

    if we add these to equations we can eliminate the y part

    61x = 122 therefore

    x = 2

    once we have one variable, we can substitute it on either equation to get y

    lets take the first original equation
    7(2) + 4y = -2, from here
    4y = -16 and
    y = -4

    bwt, these are first order equations.

    good luck with your math
    Sharpe's Avatar
    Sharpe Posts: 8, Reputation: 1
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    #3

    Jul 5, 2007, 08:06 PM
    Thank you!!
    s_cianci's Avatar
    s_cianci Posts: 5,472, Reputation: 760
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    #4

    Jul 6, 2007, 05:03 PM
    After getting x = 2, just go back to either 7x + 4y = -2 or 10x - 3y = 32, plug the 2 in for x and solve for y.

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