Given the identity

prove

for .

* Proof. * Starting with the given identity we sum over ,

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#
Stumbling Robot

A Fraction of a Dot
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Prove a formula for the sum from k=1 to n of cos kx

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### Point out an error, ask a question, offer an alternative solution (to use Latex type [latexpage] at the top of your comment):

Given the identity

prove

for .

* Proof. * Starting with the given identity we sum over ,

looks like a part of the second line is missing