By assuming the time-dependent fields E = E_oe^{j(k ∙ r - wt)} and H = H_oe^{j/(k ∙ r - wt)} where k = k_xa_x + k_ya_y + k_za_z is the wave number vector and r = xa_x + ya_y + za_z is the radius vector, show that ∆ × E = – ∂B/∂t can be expressed as k × E = μwH and deduce a_k × a_E = a_H.