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Trignometry

Cool goIITian

Joined:	11 Jul 2007
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12 Jul 2007 14:12:58 IST

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798

principal function

None

4sinxsin2xsin4x=sin3x at x=pie/9 then 4cosxcos2xcos4x=y at pie/9 then what is the value of y?

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Nivedh Iyer

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Joined: 5 Jul 2007

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12 Jul 2007 14:31:10 IST

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is it 0.5...................................................please do rate me if i am right

Krishna Gopal Singh

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Joined: 29 Dec 2006

Posts: 5153

18 Jul 2007 20:13:55 IST

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Nivedh_89 it is 0.5 only (i chcked on calculator) but i am unable to solve this. Can u please explain how u got that

Titun

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Joined: 23 Dec 2006

Posts: 374

18 Jul 2007 20:44:19 IST

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y = 4cosx cos 2x cos 4x

We have to calculate the value of y at x = pie / 9 i.e at x = 20 deg

Therefore, at x = 20 deg,

y = 4 cos 20 cos 40 cos 80

i.e 2 y sin 20 = 4. (2sin20.cos20) cos 40. cos 80

i.e 2ysin 20 = 2 . (2 sin 40.cos 40) cos 80 = 2 sin 80. cos 80 = sin 160 = sin 20

i.e 2y sin 20 = sin 20 i.e y = 1/2 at x = 20 degrees.

Cheers!!!

Nivedh Iyer

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Joined: 5 Jul 2007

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19 Jul 2007 11:26:13 IST

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titun....thats absolutely perfect......

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