FindRoot

FindRoot[f, {x, x0}] searches for a numerical root of f, starting from x = x0.

FindRoot[lhs == rhs, {x, x0}] searches for a numerical solution to the equation.

Examples

Find a root:

FindRoot[Cos[x] == x, {x, 0.5}]
(* {x -> 0.739085} *)

Multivariate:

FindRoot[{x + y == 3, x - y == 1}, {{x, 1}, {y, 1}}]
(* {x -> 2., y -> 1.} *)

Please visit the official Wolfram Language Reference for more details.