examples of Lagrangian submanifolds

1. Suppose $M$ is a manifold, and $f:M\to ℝ$ is a smooth function.Then

   $$\{(df)(x)\in T_x^{\ast }(M):x\in M\}$$

   is a Lagrangian submanifold of the cotangent bundle $T^{\ast }M$ whenthis is equipped with the canonical symplectic structure.