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Homework Help: Algebra Problem

  1. Oct 4, 2007 #1
    A problem in my textbook shows
    25/9(20-y)^2 = 144+(20-y)^2
    Then the very next step shows

    Maybe its just me, but I can't seem to figure out the algebra behind this step in the problem, any ideas on where to start? I thought about subtracting/dividing the (20-y)^2 from the right side, but that seems to be getting me nowhere.
  2. jcsd
  3. Oct 4, 2007 #2


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    (20-y)^2=(9/9)(20-y)^2. You just need a common denominator.
  4. Oct 4, 2007 #3
    Thanks, not sure why but I didn't even thing about the 9 being in the denominator in the first term. Probably because of the way it was written.
  5. Oct 5, 2007 #4


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    Dearly Missed

    No, the main reason why students overlook this sort of thing, is that they don't consider an expression like (20-y)^2 as JUST ANOTHER NUMBER, but as something far more etheral and mysterious.
  6. Oct 5, 2007 #5


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    If it was actually written 25/9(20-y)^2 in your book then I can see your confusion. What you give means
    but you might confuse it with
    I can see no good reason for not using the "clear" form in a printed text book.
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