prove that: cos(2pi/2n+1)+cos(4pi/2n+1)+cos(6pi/2n+1)+...+cos(2npi/2n+1)=-1/2

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- May 9th 2011, 05:26 PMralphjason007Cosine Summation Identity
prove that: cos(2pi/2n+1)+cos(4pi/2n+1)+cos(6pi/2n+1)+...+cos(2npi/2n+1)=-1/2

- May 9th 2011, 07:41 PMTheCoffeeMachine
- May 17th 2011, 07:52 AMred_dog
Let

Multiply both members with

Using the identity we have

Then

Substitute with

Then