6.76. The solution of the Schrödinger equation should be sought in the form Ψ=ψ(x)⋅f(t). The substitution of this function into the initial equation with subsequent separation of the variables x and t results in two equations. Their solutions are ψ(x)∼eikx, where k=2mE/ℏ,E, is the energy of the particle, and f(t)∼∼e−iωt, where ω=E/ℏ. Finally, Ψ=aei(kx−ωt), where a is a certain constant.