Hi there. I am having trouble finding an explanation with waves. Suppose that you have to sinusoidal waves y1=Asin(kx-wt) and y2=Asin(kx-wt+phi) If we add them up, the resulting wave will be y=2Acos(phi/2)sin(kx-wt+phi/2). Now, if phi equals pi then the resulting wave will have no amplitude. We know that in order to cause both waves energy is needed, and that energy is proportional to the square of the amplitude. I cannot find to explain what happens to the energy. Where does it go? Wouldn't this violate the principle of the energy conservation? I appreciate any help Thanks!