It is convenient to represent waves using exponential functions. For example a stationary wave can be described by the function: ψ(x) = Aeikx, where the constant A is a real number. The function ψ(x) can be resolved into its real and imaginary parts using Euler's equation, ei θ = cosθ + isinθ, to obtain ψ(x) = Acos(kx) + iAsin(kx). A travelling stationary wave can be described by exponential function ψ(x),(t) = Aei(kx - ωt) eA + eB = eA + B