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How to determine when a function changes sign?

  1. Sep 21, 2007 #1
    Hi all.
    Say, I have an alegebric function, e.g. f(y;a)=y^4+b*y^3+c*y^2+d*y+e,
    where the coefficients b,c,d and e are all depends on a single parameter, a.

    What I want to do is to check what is the condition of a for the function f(y;a) to change its sign between 0 and 1+a, do you have any idea to do so?
    Last edited: Sep 21, 2007
  2. jcsd
  3. Sep 21, 2007 #2
    i don't understand your notation, what does f(y:a) mean?
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