If they didn't already tell you the answer, IMO it isn't an easy question for a beginner. I'm assuming the light waves are at the same frequency, but they don't specify that. Perhaps being at different frequencies is one of the answers. Another answer could be that they are at the same frequency, but traveling in different directions. A 3rd answer could be that they have the same frequency but different polarizations and are traveling through a birefringent material.## \\ ## In general, the Homework Helpers are not supposed to supply the answer, but this question seems to lack definition, and I'm not sure that the answers that I gave are even correct. I'm giving them more as a suggestion than actually as being the correct answer. ## \\ ## I'm open to suggestions for what others may think are good answers to this question.