quadratic, mathematical expression of the second degree in one or more unknowns (see polynomial). The general quadratic in one unknown has the form ax2+bx+c, where a, b, and c are constants and x is the variable. A quadratic equation ax2+bx+c=0 always has two roots, not necessarily distinct; these may be real or complex (see number). The quadratic formula
CE5
gives the roots of any quadratic equation in terms of its coefficients a, b, and c. The expression b2−4ac 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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