Use the method of separation of variables to solve the 1-dimensional wave equation
uxx = 1/16utt over x ∈ (0,4), t ∈ (0,∞), for the boundary conditions
u(0,t) = u(4,t) = 0 and initial conditions u(x,0) = 12 sin(2πx) - 6 sin(8πx) and
ut(x,0) = 0. Choose K as negative, say K = -λ^2 (for the separation constant).