fundamental theorem of algebra
The fundamental theorem of algebra is the result that every algebraic equation of the nth degree
a0xn + a1xn-1 + ... + an-1x + an = 0
whose coefficients are real numbers possesses at least one real or complex root. An algebraic equation of the nth degree with one unknown, and real coefficients, possesses exactly n roots, provided every solution (real and complex) is counted according to its mutliplicity.