Hey! In my calculus book they claim that a second degree polynomial always can be rewritten as x^2 - a^2 or as x^2 + a^2, if you use an appropriate change of variable. I was thinking about how this works. Let's say we have a second degree polynomial (on the general form?) ax^2 +bx + c = 0, then I can of course rewrite it as (x + (b/2a))^2 - (b/2a)^2 + c/a = 0. My question is if they mean that (x + (b/2a)) = u, and (b/2a)^2 + c/a = k, so we always can write it like either u^2 - k^2 or u^2 + k^2 depending on if k correpsonds to a postive or negative number? Sorry if my explanation sucks but hope you understand what I mean! Thanks!