How to determine when a function changes sign?

1. Sep 21, 2007

hanson

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. Sep 21, 2007

ice109

i don't understand your notation, what does f(y:a) mean?