There are five major classes of plant hormones (a.k.a. Plant growth regulators (Pgr's)) with perhaps a few others as candidates to take that place in the future. The five major hormone classes are Auxins[?], Cytokinins[?](CK’s), Ethylene, Gibberellins[?] (GA’s), and Abscisic Acid (ABA). Recently it has been suggested that Brassinosteroids[?] (BA’s), Jasmonates[?] (JA’s), Salicylates[?] (SA’s), and Polyamines[?] are new classes of major hormones.
... is to add a constant (i.e., in this case, a quantity that does not depend on x) to the expression to the left of "=", that will make it a perfect square trinomial of ...