Incomplete quadratic equations and how to solve them

A quadratic equation in which at least one of the coefficients b or c is zero is called incomplete. There are three types. 1) ax² = 0: x² = 0, the only root is x = 0. 2) ax² + c = 0 (c ≠ 0): x² = -c/a; if -c/a > 0 there are two roots x = ±√(-c/a), and if -c/a < 0 there is no real root. 3) ax² + bx = 0 (b ≠ 0): take x out of the brackets, x(ax + b) = 0; the roots are x₁ = 0 and x₂ = -b/a. It is easier to solve these equations by such methods than by the discriminant formula.