please give explanations and show all the steps

Problems Chapter 17 of "Physics for Scientists and Engineers", 10th ed. by Serway and Jewett. Two sound waves arrive at your ear simultaneously; they have slightly different frequencies: wj and w2 and equal amplitudes. You hear the loudness oscillate sinusoidally; this is what we refer to as "beats". Show that the total sound wave has the the form: P(t) = Patm + 28P cos( (w1 - W2) /2) cos( (w1 + w2)/2). (1) You can use the trig identity in the text on p#.470 as a guide, but take the time to derive the iden- tity using de Moivre's theorem to apply the trick we've been developing in class for trig identities