19.` cos^2 5 + cos^2 10+ cos^215 + ... + cos^2 360º =1) 18 2)27 3)364345

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

The value of cos^2 5^@ + cos^2 10^@ + cos^2 15^@ + cos^2 20^@+ cos^2 70^@ + cos^2 75^@+ cos^2 80^@ + cos^2 85^@ is equal to

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

Value of cos^(2) 5^(@) + cos^(2) 10^(@) + cos^(2) 80^(@) + cos ^(2) 85^(@) is

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

cos ^ (2) 10 ^ (@) + cos ^ (2) 50 ^ (@) + cos ^ (2) 70 ^ (@) =

cos^(2)5^(@) +cos^(2)10^(@) + cos^(2) 15^(@) +…..+cos^(2) 85^(@) + cos^(2) 90^(@) is equal to

cos^(2)5^(@)+cos^(2)10^(@)+cos^(2)15^(@)+.....+cos^(2) 90^(@)=

cos^(2)5^(@)+cos^(2)10^(@)+cos^(2)15^(@)+..+cos^(2)355^(@)

Prove that : cos A cos 2A cos 2^2 A cos 2^3 A........ cos 2^(n-1) A= (sin 2^n A)/(2^n sinA) .