quadratic, mathematical expression of the second degree in one or more unknowns (see polynomial). The general quadratic in one unknown has the form ax 2+ bx + c, where a, b, and c are constants and x is the variable. A quadratic equation ax 2+ bx + c = 0 always has two roots, not necessarily distinct; these may be real or complex (see number). The quadratic formula;e21;none;1;e21;;;block;;;;no;1;4224n;242407n;;;;;eq21;comptd;;center;stack;;;;;CE5gives the roots of any quadratic equation in terms of its coefficients a, b, and c. The expression b 2 - 4 ac is called the discriminant and vanishes when the two roots coincide. If a, b, and c are real and the discriminant is not less than zero, the roots are real.