Prove that:

4 cosA cos(60-A) cos(60+A) = cos3A

 

Hence proved.

  • 18

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

  • 20
What are you looking for?