Discriminant

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In algebra, the discriminant of a polynomial that is equal to zero with real or complex coefficients is a certain expression in these coefficients of the polynomial if and only if the polynomial has a multiple root (for example, a root with multiplicity greater than one) in the complex numbers.

For example, the discriminant of the quadratic polynomial

ax^2+bx+c\,       is       \,b^2-4ac.