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Expanding (cos x + i sin x)^2 and comparing real parts gives cos 2x equal to what?
A1 − 2 cos^2 x
Bcos^2 x − sin^2 x
Ccos^2 x + sin^2 x
D2 sin x cos x
Answer & Solution
Correct answer: B. cos^2 x − sin^2 x
The real part of cos^2 x + 2i sin x cos x − sin^2 x is cos^2 x − sin^2 x.
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