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■ >0: 3⁄2x2+1⁄2x−4⁄3 In the above formula, the expression underneath the square root sign is called the discriminant of the quadratic equation, and is often represented using an upper case D or an upper case Greek delta, the initial of the Greek word Διακρίνουσα, Diakrínousa, discriminant: A quadratic equation with real coefficients can have either one or two distinct real roots, or two distinct complex roots. In this case the discriminant determines the number and nature of the roots. There are three cases: If the discriminant is positive, then there are two distinct roots, both of which are real numbers: For quadratic equations with integer coefficients, if the discriminant is a perfect square, then the roots are rational numbers—in other cases they may be quadratic irrationals. If the discriminant is zero, then there is exactly one distinct real root, sometimes called a double root: If the discriminant is negative, then there are no real roots. Rather, there are two distinct (non-real) complex roots, which are complex conjugates of each other: where i is the imaginary unit. Thus the roots are distinct if and only if the discriminant is non-zero, and the roots are real if and only if the discriminant is non-negative. Monic form:Dividing the quadratic equation by the quadratic coefficient a gives the simplified monic form of where p = b/a and q = c/a. This in turn simplifies the root and discriminant equations somewhat to