Find the value of `cos(2pi)/7+cos(4pi)/7+cos(6pi)/7`

Find the value of 2cos^3(pi/7)-cos^2(pi/7)-cos(pi/7)

Find the value of cos^(-1)(cos""(pi)/(7)cos""(pi)/(17)-sin""(pi)/(7)sin""(pi)/(17))

Find the value of (cos .pi/7 cos . pi/17 - sin .pi/7 sin . pi/17)

The value of cos(pi/7)+cos((2pi)/7)+cos((3pi)/7)+cos((4pi)/7)+cos((5pi)/7)+cos((6pi)/7)+cos((7pi)/7) is 1 (b) -1 (c) 0 (d) none of these

Find the value of cos^(-1)(cos . (5pi)/9 cos .pi/9 - sin . (5pi)/9 . sin. (pi)/9 )

Find the value of cos^(-1)(cos((4pi)/(3)))+cos^(-1)(cos((5pi)/(4)))

Find the value of cos^2pi/(16)+cos^2(3pi)/(16)+cos^2(5pi)/(16)+cos^2(7pi)/(16)dot

Find the value of sin^(-1) (sin . (5pi)/8 cos . (pi)/8 - cos . (5pi)/8 sin. (pi)/8)