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secondary 4 | A Maths
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secondary 4 chevron_right A Maths chevron_right Singapore

Help me solve 11d please. Thanks in advance.

Date Posted: 5 months ago
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Eric Nicholas K
Eric Nicholas K's answer
2980 answers (Tutor Details)
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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.