If the amplitude varies slowly as compared to the phase A 0 ( x ) = 0 and B 0 ( x ) = ± ± 2 m ( E − − V ( x ) ) which corresponds to classical motion. Resolving the next order of expansion yields Ψ Ψ ( x ) ≈ ≈ C e i ∫ ∫ d x 2 m ℏ ℏ 2 ( E − − V ( x ) ) + θ θ 2 m ℏ ℏ 2 ( E − − V ( x ) ) 4