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Math Help - Non-linear system of two equations

  1. #1
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    Non-linear system of two equations

    This is what I was given:
    x+y=11
    x - y = 77

    I need to find x. How do I do this?
    Do I square the x+y=11 and then add the two equations to find x?
    Last edited by jjkk5522; October 2nd 2010 at 06:50 PM.
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  2. #2
    Senior Member Educated's Avatar
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    Use the substitution method to solve this simultaneous equation.

    Rewrite one of the equations as y=... and then substitute this into the second equation everytime y occurs.
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  3. #3
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    Find out what x or y equals in one of the equations and then substitute it into the second equation. This gives you the value of one variable. Then just plug that value into one of the original equations to find the other variable:

    EX:
    x + y = 10
    2y - 2x = 0

    x = -y + 10
    2y - 2(-y + 10) = 0
    2y + 2y - 20 = 0
    4y = 20
    y = 5
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  4. #4
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    so it should look like this?

    y=-x+11
    x-(-x+11)=77
    x+x-121=77
    2x=198
    x=99
    x is about 9.95?
    but the real answer is supposed to be x=9.
    what did i do wrong?
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  5. #5
    Senior Member Educated's Avatar
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    You expanded the brackets (-x+11) wrong.

    Remember: (a+b) = a * 2ab * b
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  6. #6
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    Thank you for the help. I finally get it now.
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