hi

i have little problem here with this problem

i have to find a formula for this sum serie

1+cos(x)+cos(2x)+cos(3x)+....+cos(nx)

the hint is i have to use sum of geometric series with the general term e^(ikX)

thanks

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- Nov 14th 2009, 12:41 PM #1

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- Nov 14th 2009, 03:23 PM #2

- Nov 14th 2009, 11:25 PM #3

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- Nov 14th 2009, 11:29 PM #4
good job. the trick of course was to realize that your sum is the real part of the sum $\displaystyle \sum_{k = 0}^\infty e^{i(kx)}$, which can be interpreted as a geometric series for which you know the formula.

just for fun (and curiosity) what other ways were you thinking of, Kriz?

- Nov 15th 2009, 12:01 PM #5

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