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-   -   How do I solve using eliminations? (https://www.askmehelpdesk.com/showthread.php?t=486424)

  • Jul 8, 2010, 06:49 AM
    Kiwiwalter
    How do I solve using eliminations?
    3x+4y=-1, -9x-4y=-1
  • Jul 8, 2010, 06:52 AM
    Curlyben
    Nice and simple really.
    Make x the subject in one of the equations then plug that value into the second.
  • Jul 8, 2010, 07:03 AM
    MathMadMan
    Homework?

    First, tell us what the eliminations method is, then you'll see that the answer is right there.
  • Jul 8, 2010, 07:14 AM
    Kiwiwalter
    Well I don't really know because this is the first time I've ever seen this problem...
  • Jul 8, 2010, 07:31 AM
    MathMadMan
    Ok, by example:

    4x + 3y = -5
    2x - y = 5

    Using the elimination method you multiple the second equation (both sides of it) by 3. This will make the -y in the second become -3y, so that when you add the two equations together, the y terms will cancel out.

    Multiplying both sides of second equation by 3...
    3(2x - y) = 3 x 5 => 6x - 3y = 15

    This results in this pair of equations

    4x + 3y = -5 <= the original first equation
    6x - 3y = 15 <= new second equation

    Adding them together (3y + -3y = 0)...

    10x = 10

    And thus x = 1

    To solve for y, plug x=1 into the first equation (you could choose the second equation, just pick what looks easier)

    4 + 3y = -5
    3y = -9
    y=3


    So, in the elimination method, your goal is to get rid of one of the variables by multiplying or dividing one of the equations by a constant value and then adding the two equations together. If the equations already have equal but opposite terms, just add them together and solve for the remaining variable.

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