Answer :

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.

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