`cos(pi)/(8)+cos(3 pi)/(8)+cos(5 pi)/(8)+cos(7 pi)/(8)`

cos^4(pi/8)+cos^4((3pi)/8)+cos^4((5pi)/8)+cos^4((7pi)/8)=

Prove that: cos^4(pi/8)+cos^4((3pi)/8)+cos^4((5pi)/8)+cos^4((7pi)/8)=3/2

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

The value of (1+cospi/8)(1+cos(3pi)/8)(1+cos(5pi)/8)(1+cos(7pi)/8)i s (a)1/4 (b) 3/4 (c) 1/8 (d) 3/8

Prove that: (1+cos. (pi)/8)(1+cos. (3pi)/8)(1+cos. (5pi)/8)(1+cos. (7pi)/8)=1/8

Prove that cos(2pi)/(15)cos(4pi)/(15)cos(8pi)/(15)cos(14pi)/(15)=1/(16)

The equation x^3=3/4x=-(sqrt(3))/8 is satisfied by x=cos((5pi)/(18)) (b) x=cos((7pi)/(18)) x=cos((23pi)/(18)) (d) x=cos((17pi)/(18))

Prove that: 2cos pi/(13) cos (9pi)/(13) +cos (3pi)/(13) +cos (5pi)/(13)=0

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

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