`2cos(pi/13)cos(9pi/13)+cos(3pi/13)+cos(5pi/13)=0`

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

Prove that: 2cos (pi)/(13) cos (9 pi)/(13)(3 pi)/(13)(5 pi)/(13)=0

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

2cos ""(pi)/(13)cos""(9pi)/(13)+cos""(3pi)/(13)+cos""(5pi)/(13)= ................ A) -1 B) 0 C) 1 D) 1/2

The value of 2"cos"(pi)/(13)"cos"(9pi)/(13)+"cos"(3pi)/(13)+"cos"(5pi)/(13) is

The expression cos ((10pi)/13)+cos ((8pi)/13)+cos ((3pi)/13)+cos ((5pi)/13) is equal to............... A) -1 B) 0 C) 1 D) None of these