(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.