For example cos(x)+cos(2x)+...+cos(n-1)x

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- Jan 8th 2013, 02:22 AMRower93How does one find the sum of series by multiplying through
For example cos(x)+cos(2x)+...+cos(n-1)x

- Jan 8th 2013, 02:38 AMJJacquelinRe: How does one find the sum of series by multiplying through
Use the identity cos(a)=(exp(ia)+exp(-ia))/2 which transforms the sum into geometric series.

- Jan 8th 2013, 02:58 AMRower93Re: How does one find the sum of series by multiplying through
The hint is 2sin(x/2). Do I begin by just multiplying every term by that.. I don't know how to start.