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Three equations, three unknowns

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    x+3y=2
    -2x+3y+z=-1
    y+z=-1

    z=-1-y
    x=2-3y

    -2(2-3y)+3y+(-1-y)=-1
    8y-5=-1
    y=2

    z=-1-2
    z=-3

    x=2-3(2)
    x=-4

    Can anyone see where I have gone wrong as my answers do not match the equations if plugged back in.
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    (Original post by Gorrilaz)
    x+3y=2
    -2(2-3y)+3y+(1-y)=-1
    8y-5=-1
    You messed up here.

    When you multiply out the brackets, you should have gotten:
    -4 + 6y + 3y + 1 - y = -1

    which simplifies to

    8y - 3 = -1
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    (Original post by FloydHead)
    You messed up here.

    When you multiply out the brackets, you should have gotten:
    -4 + 6y + 3y + 1 - y = -1

    which simplifies to

    8y - 3 = -1
    No sorry it was actually-4+6y+3y-1-y=-1

    As z=-1 -y I just write that part wrong.
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    (Original post by Gorrilaz)
    8y-5=-1
    y=2
    Your mistake is above. 8*2 does not equal 4.
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    (Original post by F1Addict)
    Your mistake is above. 8*2 does not equal 4.
    Haha wow how did it take me so long to spot.
    Thanks for your help
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    (Original post by Gorrilaz)
    Haha wow how did it take me so long to spot.
    Thanks for your help
    You're welcome.

    Sometimes the simplest things are hardest to spot.
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    Unless I'm badly mistaken, you can find all 3 variables from the first 3 equations given. Or is this one of those questions where you have to do it a given way?
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    (Original post by AtomSmasher)
    Unless I'm badly mistaken, you can find all 3 variables from the first 3 equations given. Or is this one of those questions where you have to do it a given way?
    The equations after the first 3 are working out, they're just rearranged to make x and z in terms of y.
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    I've been trying this another way but I just can't get to y = 2. Even when I put y = 2 to get x and z I get values that don't work out. Where am I going wrong?! Are y'all sure these equations are self consistent?????
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    (Original post by fire sale)
    I've been trying this another way but I just can't get to y = 2. Even when I put y = 2 to get x and z I get values that don't work out. Where am I going wrong?! Are y'all sure these equations are self consistent?????
    y=0.5 i did it wrong lol

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Updated: May 7, 2012
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