1. Solve the initial-boundary value problem using separation of variables. ² u 8² u = 9 at² əx² for 0 0 u(0, t) = 0, u(4, t) = 0 for t≥ 0 dul u(x, 0) = 2 sin(x), atl t=0 = 0 for 0≤x≤ 4.