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Homework Help: Solution to a problem

  1. Sep 27, 2010 #1

    MacLaddy

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    Gold Member

    1. The problem statement, all variables and given/known data

    Okay, so I just got home a few moments ago from the first of two midterms that I will have to take this year, (do the math on that one) and I can not seem to figure out the very first problem that was listed on the test.

    It was

    x + [tex]\sqrt{x}[/tex] = 90


    2. Relevant equations

    It says "List all solutions"

    3. The attempt at a solution

    I tried several things, but none that seemed to fit correctly. Just by looking at it I can see that one of the solutions is x=81, but I can't get it to spit that out algebraically.

    I've isolated the radical, then squared both sides to give myself a quadratic, but when I solve that I get two answers that do not work.

    I'm sure this is an easy question, and one that I should know. It will probably wake me up in the middle of the night, but it's driving me crazy for now.
     
  2. jcsd
  3. Sep 27, 2010 #2

    MacLaddy

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    Gold Member

    Oh good grief... I got it.

    I wasn't squaring 90-x together and foiling.

    x = (90-x)^2

    I was squaring them individually

    x = 8100+x^2
     
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