Two monochromatic waves emanating from two coherent sources have the displacements represented by Y1 = a cos?t and Y2 = a cos (?t + ?) , where ? is the phase difference between the two waves. Show that the resultant intensity at a point due to their superposition is given by I = 4E cos2?/2, where E= a2. Hence, obtain the condition for constructive and destructive interference