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If x+2y=2 and (x+y)2=9, what is the value of y?

  1. Jul 9, 2004 #1

    Monique

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    If x+2y=2 and (x+y)2=9, what is the value of y?

    And the answer is not -1.. what is the trick here that I'm missing? The answer is supposed to be 5.
     
  2. jcsd
  3. Jul 9, 2004 #2

    NateTG

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    [tex]x+2y=2[/tex]
    so
    [tex]x=2-2y[/tex]
    so
    [tex](x+y)^2=(2-2y+y)^2=(2-y)^2=9[/tex]
    square root of both sides:
    [tex]\pm (2-y)=3[/tex]
    [tex]-3=2-y[/tex] or [tex]3=2-y[/tex]
    So the solutions (note the plural) are:
    [tex](-8,5)[/tex] and [tex](4,-1)[/tex]

    I'm guessing you forgot that every number has two square roots. ;)
     
  4. Jul 9, 2004 #3

    Monique

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    ahhh see? these little simple things.. thanks NateTG!

    I should be doing other things at 2 in the morning :grumpy:
     
  5. Jul 10, 2004 #4
    monique is a cutie :blush:
     
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