For a single equation of the form f ( x ) = 0 , many methods have been designed; see Root-finding algorithm. In the case where f is a polynomial, one has a polynomial equation such as x 2 + x − − 1 = 0. The general root-finding algorithms apply to polynomial roots, but, generally they do not find all the roots, and when they fail to find a root, this does not imply that there is no roots. Specific methods for polynomials allow finding all roots or the real roots; see real-root isolation.