Algebraic solution

An algebraic solution is a closed form expression, and more specifically a closed-form algebraic expression, that is the solution of an algebraic equation in terms of the coefficients, relying only on addition, subtraction, multiplication, division, and the extraction of roots (square roots, cube roots, etc.).

The most well-known example is the solution

introduced in secondary school, of the quadratic equation

(where a ≠ 0).

There exist more complicated algebraic solutions for the general cubic equation^[1] and quartic equation.^[2] The Abel-Ruffini theorem^[3]:211 states that the general quintic equation lacks an algebraic solution, and this directly implies that the general polynomial equation of degree n, for n ≥ 5, cannot be solved algebraically. However, under certain conditions algebraic solutions can be obtained; for example, the equation can be solved as

Algebraic solutions form a subset of closed-form expressions, because the latter permit transcendental functions (non-algebraic functions) such as the exponential function, the logarithmic function, and the trigonometric functions and their inverses.

See also

• Solvable sextics
• Solvable septics

References