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Math Help - Solving system of equations by addition

  1. #1
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    Solving system of equations by addition

    Solve the system of equations by the addition method:
    4x-3y=-28
    3x+2y=-4

    I know the answer is 4,-4, however, how do I figure out what number comes first when completing the answer, is it (4,-4) or (-4,4). Thanks.
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  2. #2
    Super Member Quacky's Avatar
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    The ' x' value comes before the y value usually - just think of coordinates.
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  3. #3
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    Is x the input and y the output or vice versa?
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  4. #4
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    Quote Originally Posted by poirot View Post
    Is x the input and y the output or vice versa?
    X is the input, y is the output
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  5. #5
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    4x-3y=-28
    3x+2y=-4

    Multiply the top by 3 and the bottom by -4

    So we now get,

    3(4x-3y=-28) and
    -4(3x+2y=-4)

    So we now have

    12x - 9y = -84
    -12x -8y = 16

    Now if we add the 2 equations together you'll notice that the x's cancel.

    So -17y = -68

    Now solve for y

    y = -4

    Since we now know that y = -4, Plug it into either of the original given equations, I'm going to plug it into the first one for you.

    4x-3y=-28 where y = -4

    So we now have 4x - 3(-4) = -28

    Solve for x and you'll get x = -4

    So if x = -4 and y = 4

    We can write it as (-4, 4)

    Hope that helps boss. (:
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