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    mrsyidrocks's Avatar
    mrsyidrocks Posts: 1, Reputation: 1
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    #1

    Feb 3, 2009, 06:37 PM
    Algebra I - substitution
    I need help trying to understand how to solve each system by substitution here are my problems for homework tonight

    x=y-8
    -x-y=0

    x+-2y+8
    x+3y=12

    y=-x-2
    y=7x+2

    x+-y+1
    -4x+4y=12

    x=7-2y
    2x+y=5

    :confused::confused:
    bones252100's Avatar
    bones252100 Posts: 253, Reputation: 29
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    #2

    Feb 3, 2009, 07:26 PM

    x=y-8 You know that x= (y-8); Substitute (y-8) for X in the next equation

    -x-y=0 This, when solved gives you the value of Y. Substitute this value for Y in the
    next equation.

    x+-2y+8 Remember that two negatives cancel each other. This, when solved, gives
    x+3y=12 you the value of X. Plug both values into the 1st equations to check answer
    --------------------------------------------------------------------------------------------------------
    y=-x-2 Use the same procedure
    y=7x+2

    x+-y+1
    -4x+4y=12
    --------------------------------------------------------------------------------------------------------
    x=7-2y Only the second equation gives a numerical value. Plug the value of X into
    2x+y=5 this equation to solve the value of Y. Plug the value of Y into the first
    equation to solve the value of X. (Plug = Substitute)

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