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Math Help - Simultaneous Equation Help

  1. #1
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    Simultaneous Equation Help

    Hello,

    What is the value of x that satisfies the following simultaneous equation:

    x - y = - 2

    5x + 8y = - 23

    I have never been excellent at maths. So this might be the simplest simultaneous equation for you but for me I have no clue. I did do some prior research (again might sound like a dummy) and here's what I got on how to solve it:

    5x + 8(x+-2) = -23
    5x + 8x+-16 = -23
    13 + -16 = - 23
    13x + 16 = -23
    5x = - 23

    Please help!
    Last edited by Samuel554; July 29th 2014 at 06:28 PM.
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  2. #2
    Forum Admin topsquark's Avatar
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    Re: Simultaneous Equation Help

    Quote Originally Posted by Samuel554 View Post
    Hello,

    The problem is to find the value of X:

    x - y = - 25x + 8y = - 23
    Are you saying you have the two equations
    x - y = -23
    and
    -25x + 8y = -23

    Your work indicates something else. Can you please rewrite your question? This makes no sense.

    -Dan
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    Re: Simultaneous Equation Help

    My working was from another site, I don't think I was on the right track so if it's wrong just ignore it :P
    I updated the OP, my mistake I forgot to space it out. And yes it's two equations. I included the actual question if it helps. Thanks!
    Thanks from topsquark
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  4. #4
    Senior Member sakonpure6's Avatar
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    Re: Simultaneous Equation Help

    x - y = - 2 , y = x+2

    5x + 8y = - 23

    So, 5x + 8(x+2) = -23
    5x + 8x +16 = -23
    13x = - 39
    x= -3
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  5. #5
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    Re: Simultaneous Equation Help

    Another way to do this problem is to multiply the first equation by 8 to get 8x- 8y= -16. The reason for doing that is to get "-8y" which will cancel the "+8y" in the second. Adding the equation 8x- 8y= 16 to 5x+ 8y= -23 gives (8x+ 5x)+ (-8y+ 8y)= -16- 23 or 13x= -39. Now divide both sides by 13 to get x= -3.

    Once you have x= -3, the equation x- y= -2 becomes -3- y= -2 or, adding 3 to both sides, -y= 1.
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