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

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

Prove that cos pi/15 * cos 2pi/15* cos3pi/15 ... . . to 7 factors = 1/2^(7) .

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

Prove that 4cos((2pi)/7).cos(pi/7)-1=2cos((2pi)/7) .

Prove that 4cos(2 pi)/(7)*cos(pi)/(7)-1=2cos(2 pi)/(7)

prove that 4(cos(2 pi))/(7)*(cos pi)/(7)-1=2(cos(2 pi))/(7)

Prove that :16cos2(pi)/(15)cos4(pi)/(15)cos8(pi)/(15)cos16(pi)/(15)=1

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

Prove that: cos(pi/4+A)+cos(pi/4-A)=sqrt(2)cosA