Given and

Consider the equation

Now take the LHS of the equation,

cos 3x = 4cos³ x – 3cos x

[using the formula for cos 3x = 4cos³ x – 3cos x]

From the question we know,

Substituting the known cos x values in the cos 3x expansion,

------ (1)

If we compare the RHS of the cos3x equation with the now derived equation (1) we get,

From the here we can clearly say that

Hence the answer is option B.