Prove that: 4 cosA cos(60-A) cos(60+A) = cos3A Share with your friends Share 23 Harleen Birdi answered this Hence proved. 21 View Full Answer mittal.shivam13... answered this cos(A-B)cos(A+B) = cos2B- sin2A ==> L.H.S = 4cosA (cos2A - sin260) ==> 4cosA (cos2A - 3/4)==>4cos3A -3cosA = cos3A =R.H.S .Hence proved 23
