`cos^2(pi/11) + cos^2((2pi)/11) + cos^2((3pi)/11) + cos^2((4pi)/11) + cos^2((5pi)/11)` = ?

cos(pi/11) cos((2pi)/11) cos((3pi)/11)....cos((11pi)/11)=

cos^2(pi/8) +cos^2((3pi)/8) +cos^2((5pi)/8)+cos^2 ((7pi)/8)=2

Prove: cos(pi/15)cos((2pi)/15)cos((3pi)/15)cos((4pi)/15)cos((5pi)/15)cos((6pi)/15)cos((7pi)/15) = 1/2^7

Show that cos(pi/15)cos((2pi)/15)cos((3pi)/15)cos((4pi)/15)cos((5pi)/15)cos((6pi)/15)cos((7pi)/15) = 1/2^7

"cos(pi/15)cos((2pi)/15)cos((4pi)/15)cos((8pi)/15)=k

2 cos ""(pi)/(13) cos ""(9pi)/(13) + cos ""(3pi)/(13) + cos "" (5pi)/(13) = 0.

The value of cos""(pi)/(11)+cos""(3pi)/(11)+cos""(5pi)/(11)+cos""(7pi)/(11)+cos""(9pi)/(11), is

Prove that: cos^(2)((pi)/(8)) + cos^(2)((3pi)/(8)) + cos^(2)((5pi)/(8))+ cos^(2)((7pi)/(8))=2

Show that 16cos((2pi)/(15))cos((4pi)/(15))cos((8pi)/(15))cos((16pi)/(15))=1

If P=cos(pi/19)+cos((3pi)/19)+cos((5pi)/19)+....+cos((17pi)/19) and Q=cos((2pi)/21)+cos((4pi)/21)+....cos((20pi)/21) then find P-Q