In general, Polynomial equations higher than fourth degree are incapable of algebraic solution in terms of a finite number of Additions, Multiplications, and Root extractions.
See also Cubic Equation, Galois's Theorem, Polynomial, Quadratic Equation, Quartic Equation, Quintic Equation
References
Abel, N. H. ``Beweis der Unmöglichkeit, algebraische Gleichungen von höheren Graden als dem vierten allgemein aufzulösen.'' J. reine angew. Math. 1, 65, 1826.