Q(25) Prove the following
We know that
cos 3x = 4 - 3cos x
we use this in our problem
we can write cos 6x as cos 3(2x)
cos 3(2x) = 4 - 3 cos 2x
= -
=
= 32 - 4 - 48 + 24 -
= 32 - 48 + 18 - 1 = R.H.S.