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[" 6."cos^(2)9^(0)+cos^(2)18^(0)+cos^(2)...

[" 6."cos^(2)9^(0)+cos^(2)18^(0)+cos^(2)27^(0)+......+cos^(2)81^(0)=],[[" a) "4," b) "9/2," c) "5," d) "11/2]]

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cos^(2) 9^(@)+cos^(2)18^(@)+cos^(2) 27^(@)+...+cos^(2)81^(@)=

2(cos^(2) 73^(0) +cos^(2)47^(0)) - cos 154^(0) =

cos^(2)75^(0)+cos^(2)15^(0)-cos75^(0)cos15^(0)=

cos ^ (2) 9 + cos ^ (2) 18 + cos ^ (2) 27 + .... + cos ^ (2) 81 =

cos1^(0)cos2^(0)...cos179^(@)

6cos^(3)x+cos^(2)x-1=0

cos1^(0)+cos2^(0)+cos3^(0)+ . . .+cos180^(0) =

(cos^(2)1^(0)-cos^(2)2^(0))/(2sin3^(0)*sin1^(0)) is equal to

cos ^ (2) (5 ^ (0)) + cos ^ (2) (10 ^ (0)) + cos ^ (2) (15 ^ (0)) + ...... + cos ^ (2 ) (360 ^ (@))

The value of (cos^(2)33^(0)-cos^(2)57^(0))/(sin21^(0)-cos21^(0)) is