If `A=sin((2pi)/7)+sin((4pi)/7)+sin((8pi)/7)` and `B=cos((2pi)/7)+cos((4pi)/7)+cos((8pi)/7)` then `sqrt(A^2+B^2) ` is equal to

If A=sin((2 pi)/(7))+sin((4 pi)/(7))+sin((8 pi)/(7)) and B=cos((2 pi)/(7))+cos((4 pi)/(7))+cos((8 pi)/(7)) then sqrt(A^(2)+B^(2)) is equal to

Prove that cos((2pi)/7) cos((4pi)/7) cos((8pi)/7) =1/8

cos.(2pi)/(7)+cos.(4pi)/(7)+cos.(6pi)/(7)

Prove that cos((2pi)/7)cos((4pi)/7)cos((8pi)/7)=1/8

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

Show that: sin((2pi)/7)+ sin ((4pi)/7) + sin( (8pi)/7) = sqrt7/2 .

sin ((pi) / (7)) sin ((2 pi) / (7)) sin ((3 pi) / (7))