Roots[lhs==rhs, var] yields a disjunction of equations which represent the roots of a polynomial equation.
Roots uses Factor and Decompose in trying to find roots.
You can find numerical values of the roots by applying N.
Roots can take the following options:
Roots is generated when Solve and related functions cannot produce explicit solutions. Options are often given in such cases.
Roots gives several identical equations when roots with multiplicity greater than one occur.
See The Mathematica Book: Section 1.5.7 and Section 3.4.1.
See also: Solve, NSolve, FindRoot, ToRules, Root, Factor, Decompose, InterpolatingPolynomial.
Related package: Algebra`RootIsolation`.