Question and Answers Forum
Question Number 76265 by A8;15: last updated on 25/Dec/19
Answered by Tanmay chaudhury last updated on 26/Dec/19
![S=cosα+cos2α+cos3α+...+cosnα multiply each term by 2sin((α/2)) and apply trigo formula and adding them 2cosαsin((α/2))=sin(((3α)/2))−sin((α/2)) 2cos2αsin((α/2))=sin(((5α)/2))−sin(((3α)/2)) ... ... 2cosnαsin((α/2))=sin(((2n+1)/2))α−sin(((2n−1)/2))α add them 2sin((α/2))×S=sin(((2n+1)/2))α−sin((α/2)) S=(1/(2sin((α/2))))×[sin(((2n+1)/2))α−sin((α/2))]](Q76300.png)
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Question and Answers Forum | ||
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Question Number 76265 by A8;15: last updated on 25/Dec/19 | ||
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Answered by Tanmay chaudhury last updated on 26/Dec/19 | ||
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