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Taking the real part of (cos x + i sin x)^3 yields cos 3x as what?
A4 cos^3 x − 3 cos x
B2 cos^3 x − cos x
C3 cos x − 4 cos^3 x
D3 cos^2 x − 1
Answer & Solution
Correct answer: A. 4 cos^3 x − 3 cos x
Taking the real part of (cos x + i sin x)^3 and replacing sin^2 x by 1 − cos^2 x gives 4 cos^3 x − 3 cos x.
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