A quartic equation is a fourth-order polynomial equation of the form z^4 + a_3 z^3 + a_2 z^2 + a_1 z + a_0 = 0. While some authors (Beyer 1987b, p. 34) use the term "biquadratic equation" as a synonym for quartic equation, others reserve the term for a quartic equation having no cubic term, i.e., a quadratic equation in x^2.

biquadratic equation | cubic equation | polynomial discriminant | quadratic equation | quartic formula | quintic equation