Problem (S'93, #4). The temperature T(x, t) in a stationary medium, z 0, is governed by the heat conduction equation . dr Making the change of variable (r, t)-(u,t), where u = x/2t, show that T 8T OT at du Solutions of (18.7) that depend on u alone are called similarity solutions. 68 ar t 4t- +2u- (18.6) (18.7)