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Which identity gives cos (x + y)?
Asin x cos y − cos x sin y
Bcos x cos y + sin x sin y
Ccos x cos y − sin x sin y
Dsin x cos y + cos x sin y
Answer & Solution
Correct answer: C. cos x cos y − sin x sin y
The cosine of a sum is cos x cos y minus sin x sin y, as the chord-length derivation on the unit circle shows.
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