it has a shrt cut :P
The value of
cos(2pie/7) + cos(4pie/7) + cos(6pie/7) + cos(7pie/7)
1. 1
2. -1
3. 0.5
4. -1.5
cmon guys kill it....its an easy 1 i think
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10 Answers
Manish Shankar
·2009-05-05 00:51:46
cos(2pie/7) + cos(4pie/7) + cos(6pie/7)+cos(8pie/7) + cos(10pie/7) + cos(12pie/7)=-1 (sum of roots of x7=1)
2(cos(2pie/7) + cos(4pie/7) + cos(6pie/7))=-1
cos(2pie/7) + cos(4pie/7) + cos(6pie/7)=-1/2
cos(2pie/7) + cos(4pie/7) + cos(6pie/7)+cos(7pie/7)=-1/2-1=-1.5
kamalendu ghosh
·2009-05-05 06:25:54
in post #8 ...sorry i messed it up!! the formula is the same but interchange sin and cos