I THINK the definition of a trinomial = "any polynomial with three terms". So x^3 3x 4 would be a trinomial, but e.g. x^3 5x^2 3x 4 wouldn't. WHY. There is like absolutely no reason to classify polynomials like this. Like...can't we just classify them by degree instead?
HS textbks drive me bonkers in so many ways.
In factoring a quadratic expression with int coeffs (is that what a "trinomial" is?) first a) Why do we want to? and b) Have you ever questioned the "split the middle term" technique? Textbooks don't!
It's far from obvious why works.