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Which expression gives cos x in terms of complex exponentials?
A(e^ix + e^−ix)/2
B(e^ix − e^−ix)/2i
C(e^ix + e^−ix)/2i
D(e^ix − e^−ix)/2
Answer & Solution
Correct answer: A. (e^ix + e^−ix)/2
Adding e^ix = cos x + i sin x and e^−ix = cos x − i sin x leaves 2 cos x.
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