When a cubic or quartic has a double root

Thanks to the quadratic equation, it’s easy to tell whether a quadratic equation has a double root. The equation has a double root if and only if the discriminant is zero. The discriminant of a cubic is much less known, and the analogs for higher order polynomials are unheard of. There is a discriminant for […] The post When a cubic or quartic has a double root first appeared on John D. Cook....

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