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Math Help - solve by substitution

  1. #1
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    solve by substitution

    3x-2y=-11
    x=2y-9

    i got the answer x=2. Is that right?
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  2. #2
    Senior Member
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    To check your answer substitute it into each equation. Putting x = 2 into the first equation 3x-2y = -11 gives 6-2y=-11, 17=2y, y=17/2. Putting x = 2 into the second equation x = 2y-9 gives 2 = 2y-9, 11=2y, y=11/2. These are not consistent so x=2 cannot be correct.

    Write your two equations as
    3x - 2y = -11
    x - 2y = -9
    Subtract the second from the first
    2x = -11 - (-9) = -2
    x = -1

    Substitute into each equation
    -3 - 2y = -11: y = 4 and
    -1 = 2y - 9: y = 4. These are consistent. So x=-1, y=4.
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