Eric Nicholas K's answer to AX's Secondary 4 A Maths Singapore question.

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Eric Nicholas K
Eric Nicholas K's answer
5997 answers (Tutor Details)
1st
The angles 2x and x are not the same, so we must somehow change all the angles into x. This can be achieved using the double angle identity.

Because the other term is cos x, I express cos 2x in the 2 cos2x - 1 form so that I can achieve an all cos x equation to get a quadratic-like equation.