Let E(t) = NIK ut ( x, t) + ( Vu(x, t) )' dV, V where u(x, t) is a solution of at2 = V2u in a bounded domain x = (x, y, z) E V with piecewise smooth boundary OV, subject to boundary conditions Aut(, t) + B(n . Vu(x, t)) = 0, T E OV, where n is the outer unit normal to OV, and A and B are some constants at least one of which is nonzero. Determine conditions on the constants A and B which guarantee that dE/dt = 0. Also, determine conditions on the constants A and B which guarantee that dE/dt