(4-6) ① The first thing is to find the equation for the wave that’s travelling to the left. Look again at section 4-3, to remind yourself how you got the equation for the one going to the right and figure out what will be different.
② Now write down the equation for the superposed waves. You can work out what this corresponds to by using another of your trigonometric formulae:
③ Look at the expression you derive for the superposed waves. See if you can deduce what it means about the form of this product wave.