In elementary algebra letters are used to stand for numbers. For example, in the equation *ax* ^{2}+ *bx* +c = 0, the letters *a, b,* and *c* stand for various known constant numbers called coefficients and the letter *x* is an unknown variable number whose value depends on the values of *a, b,* and *c* and may be determined by solving the equation. Much of classical algebra is concerned with finding solutions to equations or systems of equations, i.e., finding the roots, or values of the unknowns, that upon substitution into the original equation will make it a numerical identity. For example, *x* = - 2 is a root of *x* 2 - 2 *x* - 8 = 0 because ( - 2)2 - 2( - 2) - 8 = 4+4 - 8 = 0; substitution will verify that *x* = 4 is also a root of this equation.

The equations of elementary algebra usually involve polynomial functions of one or more variables (see function). The equation in the preceding example involves a polynomial of second degree in the single variable *x* (see quadratic). One method of finding the zeros of the polynomial function *f* ( *x* ), i.e., the roots of the equation *f* ( *x* ) = 0, is to factor the polynomial, if possible. The polynomial *x* ^{2} - 2 *x* - 8 has factors ( *x* +2) and ( *x* - 4), since ( *x* +2)( *x* - 4) = *x* 2 - 2 *x* - 8, so that setting either of these factors equal to zero will make the polynomial zero. In general, if ( *x* - *r* ) is a factor of a polynomial *f* ( *x* ), then *r* is a zero of the polynomial and a root of the equation *f* ( *x* ) = 0. To determine if ( *x* - *r* ) is a factor, divide it into *f* ( *x* ); according to the Factor Theorem, if the remainder *f* ( *r* )—found by substituting *r* for *x* in the original polynomial—is zero, then ( *x* - *r* ) is a factor of *f* ( *x* ). Although a polynomial has real coefficients, its roots may not be real numbers; e.g., *x* 2 - 9 separates into ( *x* +3)( *x* - 3), which yields two zeros, *x* = - 3 and *x* = +3, but the zeros of *x* 2+9 are imaginary numbers.

The Fundamental Theorem of Algebra states that every polynomial *f* ( *x* ) = *a* _{ n } *x* ^{ n }+ *a* n - 1

- Introduction
- Principles of Classical Algebra
- Principles of Modern Algebra
- Bibliography

*The Columbia Electronic Encyclopedia,* 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.

- algebra: Principles of Classical Algebra - Principles of Classical Algebra In elementary algebra letters are used to stand for numbers. For ...