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Question
Express the following as the product of sine and cosine.
cos 2θ – cos θ
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Solution
cos 2θ – cos θ
`= - 2 sin ((2theta + theta)/2) sin ((2theta - theta)/2)` ...`[∵ cos "C" - cos "D" = - 2 sin (("C + D")/2) cos (("C - D")/2)]`
= - 2 sin `((3theta)/2) sin ((theta)/2)`
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