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Math Help - Please check if this is right?

  1. #1
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    Please check if this is right?

    Use substitution to solve:

    x=3y-2
    2x+4y=16


    x-3y=2
    (+)2x+4y=16
    ----------------
    3x+1y =18

    3x+1y-1y+18-y
    3x/3 = 18/3
    x=6

    6-3y=2
    6-3y+3y=2+3y
    6/6=6y/6
    y=0

    Is my answer is right?
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  2. #2
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    Quote Originally Posted by Hayabusa
    Use substitution to solve:
    x=3y-2
    2x+4y=16
    try this

    eq1 x=3y-2
    eq2 2x+4y=16

    eq2 - 2(eq1)

    ..2x+4y=16
    -2(x=3y-2)
    -----------
    0+4y=16-3y+2

    or

    4y=18-3y

    7y=18

    y=18/7, now plug in y to either equation to find x
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  3. #3
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    Quote Originally Posted by Hayabusa
    Use substitution to solve:

    x=3y-2
    2x+4y=16
    [...]
    x=6
    [...]
    y=0

    Is my answer is right?
    Well, the answer has to be 'no' as you can see by trying the values you've obtained in the original equations. For example, if x=6 and y=0 then 3y-2=-2 and this isn't equal to x, so the first equation isn't satisfied. 2x+4y=12 and so the second isn't satisfied either, but your answer would have had to be wrong even if only one of the two had failed.

    Since you're told to use substitution I think you were being asked to use x=3y-2 in the second equation, so that 2(3y-2)+4y=16 giving 10y-4=16, 10y=20, y=2 and then x=4.
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  4. #4
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    Quote Originally Posted by Math Help
    try this

    eq1 x=3y-2
    eq2 2x+4y=16

    eq2 - 2(eq1)

    ..2x+4y=16
    -2(x=3y-2)
    -----------
    0+4y=16-3y+2
    No, 0+4y = 16 - 6y+4
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