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

sum_(r=1)^(6)6C_(r)

If A=sum_(r=1)^(3)"cos"(2r pi)/(7) and B=sum_(r=1)^(3)"cos"(2^(r )pi)/(7) then :

If A= sum _(r=1)^(3)"cos"(2r pi)/(7) and B=sum_(r=1)^(3)"cos"(2^(r )pi)/(7) , then :

If A= sum _(r=1)^(3)"cos"(2r pi)/(7) and B=sum_(r=1)^(3)"cos"(2^(r )pi)/(7) , then :

Find sum_(r=1)^(10) cos^(3) rpi/3 .

Let x_1=prod_(r=1)^5cos(rpi)/(11)\ a n d\ x_2=sum_(r=1)^2cos(rpi)/(11), then show that x_1dotx_2=1/(64)(cos e c\ pi/(22)),\ w h e r e\ prod\ denotes the continued product.

Let C=sum_(r=1)^(17)cos(10r)^(@) and S=sum_(r=1)^(17)cot(10r)^(@)

Let S= sum_(r=1)^(5) cos (2r-1) (pi)/(11) and P=Pi_(r=1)^(4) cos (2^(r). (pi)/(15)) , then