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## Homework Statement

Using the condition of vector equilibrium, prove that

[tex]\sum[/tex][tex]^{2n-1}_{k=0}[/tex] cos ((k*pi)/n)

Where n is an integer.

## Homework Equations

I know that if n equal vectors are at an angle (2*pi)/n

Their resultant is zero.

## The Attempt at a Solution

Please first explain to me what does this sigma signify and what is meant by its subscript and superscript. Then please give me an idea of what to do with this problem. Thanks.

Ritwik