sum_(r=1)^(6)(sin(2 pi r)/(7)-i cos(2 pi r)/(7))=

sum_(m=1)^(32)m[sum_(k=1)^(6)sin2k(pi)/(7)-i cos2k(pi)/(7)]

sum_ (k = 1) ^ (6) (sin, (2 pi k) / (7) -i cos, (2 pi k) / (7)) =?

prod_ (k = 1) ^ (6) (sin ((2k pi) / (7)) - i cos ((2k pi) / (7))) =

sum_(r =1)^(16) ( sin [(2r pi)/(17)] + icos [(2rpi)/(17)] ) =

let a=sum_(r=1)^(6)cos((r pi)/(7)),b=sum_(r=1)^(6)cos^(2)((r pi)/(7)),c=sum_(1<=i)sum_(j<=6)cos((i pi)/(7))cos((j pi)/(7)) then find the value of (a-b)/(c)

The least positive integral value of k for which [(cos.(2pi)/(7),-sin.(2pi)/(7)),(sin.(2pi)/(7),cos.(2pi)/(7))]^(k)=[(1,0),(0,1)] is