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Ask iit jee aieee pet cbse icse state board experts Expert Question: prove that:
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[Post New]7 Apr 2008 08:09:06 IST
    Subject: prove that:
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rex_kj (0)

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cos^4/8+cos^4 3/8+ cos^4 5/8 +cos^4 7/8=3/2
 
    
[Post New]7 Apr 2008 08:47:30 IST
    Subject: Re:prove that:
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uday_zingtudor (931)

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cos4pi/8 =cos47pi/8 and cos43pi/8 =cos45pi/8

cos43pi/8 =sin4pi/8

Now the expression reduces to 2(cos4pi/8 +sin4pi/8) = 2(cos2pi/8+sin2pi/8)2-4cos2pi/8sin2pi/8 = 2 - sin2pi/4 = 2 - 1/2 =3/2

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[Post New]7 Apr 2008 09:29:15 IST
    Subject: Re:prove that:
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pantpranav (367)

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LHS = cos4 /8 + cos4 3/8 + cos4 5/8 + cos4 7/8
       = cos4 /8 + cos4 3/8 + cos4 ( - 3/8) + cos4 ( - /8)
       = 2(cos4 /8 + cos4 3/8)
       = 2(cos4 /8 + sin4 /8)
       = 2(1 - 2sin2 /8)
       = 2 - 4 sin2 /8
       = 2 - sin2 /4
       = 2 - 1/2
       = 3/2 = RHS

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[Post New]7 Apr 2008 23:04:59 IST
    Subject: Re:prove that:
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magiclko (4210)

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both the above solution are correct...
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