prove that `cos[pi/5]-cos[[2pi]/5]=1/2`

Prove that: sin(pi/10). cos(pi/5)=1/4

For A in R , prove that cos""pi/9.cos""(2pi)/9.cos""(3pi)/9.cos""(4pi)/9=1/16

Prove that: cos(pi/5)cos((2pi)/5)cos((4pi)/5)cos((8pi)/5)=(-1)/16

Prove that: (cos pi)/(5)(cos(2 pi))/(5)(cos(4 pi))/(5)(cos(8 pi))/(5)=(-1)/(6)

bb"Statement I" The range of f(x)=sin(pi/5+x)-sin(pi/5-x)-sin((2pi)/5+x)+sin((2pi)/5-x) is [-1,1]. bb"Statement II " cos""pi/5-cos""(2pi)/5=1/2

bb"Statement I" The range of f(x)=sin(pi/5+x)-sin(pi/5-x)-sin((2pi)/5+x)+sin((2pi)/5-x) is [-1,1]. bb"Statement II " cos""pi/5-cos""(2pi)/5=1/2

bb"Statement I" The range of f(x)=sin(pi/5+x)-sin(pi/5-x)-sin((2pi)/5+x)+sin((2pi)/5-x) is [-1,1]. bb"Statement II " cos""pi/5-cos""(2pi)/5=1/2

bb"Statement I" The range of f(x)=sin(pi/5+x)-sin(pi/5-x)-sin((2pi)/5+x)+sin((2pi)/5-x) is [-1,1]. bb"Statement II " cos""pi/5-cos""(2pi)/5=1/2

Prove that cos^-1 (cos ((5pi)/(3)) = pi/3

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