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 gives 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.
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