Mathematics

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26 Feb 2012 19:58:35 IST
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what is the value of sin36
CBSE Board , CBSE X , Mathematics

what is the value of sin36



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Sumiran agrawal's Avatar

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Joined: 20 Jul 2011
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28 Feb 2012 21:31:23 IST
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 We know that cos2x = 1-2sin^2x

Let x = 18

then, cos 36 = 1-2sin^2(18)

                       = 1 - 2(root5 - 1)^2/4^2

                      = (root5 + 1)/4

and also, we know that  

                                sin36 = root[ 1 - cos^2(36)]

Solving it further, you'll get sin36 = root[ 10 - 2root5] / 4


Scorching goIITian

Joined: 18 Apr 2012
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26 Jun 2012 12:38:15 IST
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 The answer given by Sumiran agrawal is nice and I have come up with the exact answer but have some problem in posting the method but the answer is -0.991778853.

 

Sumiran agrawal's Avatar

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Joined: 20 Jul 2011
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26 Jun 2012 20:25:55 IST
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How do you getting 0.99... 

The answer to this is 0.587 (approx.).




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