Quartic Equation

A quartic equation is a polynomial equation of the fourth degree, with the general form a x to the fourth power plus b x cubed plus c x squared plus d x plus e equals zero, where a is not zero. Like any fourth degree polynomial it always has exactly four roots, counting multiplicity, some of which may repeat or be complex numbers. Quartic equations are notable as the highest degree polynomial equations that can always be solved exactly using radicals, meaning ordinary arithmetic together with root extraction; the Abel-Ruffini theorem shows that no such general radical solution exists for polynomial equations of the fifth degree or higher, which makes the quartic the last case solvable by classical methods. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/