" 4."cos(pi)/(10)+cos(13 pi)/(10)

S_(10) = cos'(pi)/(180) + cos'(3pi)/(180) + "….." cos '(19pi)/(180)

The value of cos((pi)/(10))cos((2 pi)/(10))cos((4 pi)/(10))cos((8 pi)/(10))cos((16 pi)/(10))

If m and M be the minimum and maximum value of f(x)=cos((pi)/(10)+x)-cos((pi)/(10)-x)-cos((3 pi)/(10)+x)+cos((3 pi)/(10)-x) then

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

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

The value oif the expressin (1+(cos pi)/(10))(1+(cos(3 pi))/(10))(1+(cos(7 pi))/(10))(1+(cos(9 pi))/(10)) is

Prove that: (1+ cos ""(pi)/(10)) (1+ cos ""(3pi)/(10)) (1+ cos ""(7 pi)/(10)) (1+ cos""(9 pi)/(10))=(1)/(16)