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Math Help - Simultaneous equation help

  1. #1
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    Simultaneous equation help

    Okay I'm not even sure if this even is a simultaneous equation, but I don't know how to solve it anyway..

    x+y=60

    x^2 = 0.25
    y^2

    Find x and y.

    It's part of a massive a level physics question and I've simplified it a lot, so no I'm not a 12 year old asking for the answers to his maths homework :P
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  2. #2
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    Changing the second around a bit, you get the much simpler

    4x^2 = y^2

    It is now your responsibility to remember that y = 0 is inappropriate.

    If we KNOW that x and y are greater than zero (0), we get:

    2x = y

    Do we KNOW that x and y are greater than zero (0)?

    Simultaneous solution is rather simple after that.
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  3. #3
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    Yes x and y are greater than zero

    Okay thanks a lot, that did it and got the correct answer. But out of interest, how did you go from 4x^2 = y^2 to 2x = y? Is that just a general rule when x and y are greater than 0?
    Last edited by Magma828; February 18th 2010 at 10:27 AM.
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  4. #4
    A riddle wrapped in an enigma
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    Quote Originally Posted by Magma828 View Post
    Yes x and y are greater than zero

    Okay thanks a lot, that did it and got the correct answer. But out of interest, how did you go from 4x^2 = y^2 to 2x = y? Is that just a general rule when x and y are greater than 0?
    Hi Magma828,

    TK took the square root of each side of the equation.

    4x^2=y^2

    \sqrt{4x^2}=\sqrt{y^2}

    2x=y
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  5. #5
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    ... and that's why we needed to know things were positive. If things can be negative, that square root is not quite as straight forward.
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