Statement: 1. The intensity of wave A at point P is I. Intensity of wave B at point P is (4/9)I. The phase difference between these two waves 180 degrees. Wavelength of A and B is 3x10^-4 and 2x10^-4 cm respectively. Frequency of both waves is "f". What is the resultant intensity at P in terms of I? 2. Formulae: I= (Amp.)^2 x (Freq.)^2 3. An attempt: Resultant intensity = I - (4/9)I = (5/9)I My attempt is incorrect, apparently. The correct method is to first find the resultant amplitude of both the waves superposed, and then finding the intensity using a ratio. Why I can't understand is why my method is incorrect. I'll be very glad if someone clears this up for me. Thanks.