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Mathematics 18 Online
OpenStudy (anonymous):

1/2 + cos(x) + cos(2x) + ... + cos(13x) = ...?

OpenStudy (cherylim23):

Do you know complex trig identities? cos(x) = 1/2(e^xi + e^-xi) Use that to expand.

OpenStudy (anonymous):

i dont know,, any else method?

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