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cos pi/5 - cos 3pi/5 = 1/2

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gayanisam123
 
Reply Wed 19 Nov, 2014 05:56 am
cos pi/5 - cos 3pi/5 = 1/2 how can prove this by using cos pi/5 - cos 3pi/5 = 2 cos^pi/10-2 cos^pi/5
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Type: Question • Score: 0 • Views: 2,818 • Replies: 3
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engineer
 
  1  
Reply Wed 19 Nov, 2014 07:31 am
@gayanisam123,
You need to check your math problem. cos pi/5 - cos 3pi/5 does NOT equal 1/2. It needs to be cos pi/5 + cos 3pi/5. I'm not sure about that second part. Did you mean to put some exponents in there somewhere?

engineer
 
  1  
Reply Wed 19 Nov, 2014 07:55 am
@engineer,
Here is a proof for you: https://answers.yahoo.com/question/index?qid=20111017074225AAKG0Fa
StephenBotsford
 
  1  
Reply Mon 12 Jan, 2015 06:09 am
@engineer,
You just apply the formula of cosA+cosB and values cos in different angle to prove cospi/5-cos3pi/5 =1/2.
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