I know you use -b/a and c/a to find the roots, but how do i know what one to use and when? For example if they ask, "the roots of " what one do i use?
not -b/a and c/a. The sum of the roots is -b/a and the product of the roots is c/a, but you can't use that to solve the equation. (At least I've never heard of anyone doing it that way.)