`1+cos 56^0 + cos 58^0 - cos 66^0=4cos 28^0 cos 29^0 sin 33^0`.

(1+cos56^(@)+cos58^(@) -cos66^(@))/(cos28^(@)cos29^@sin33^(@)) =

Prove that : sin 51^0+cos 81^0=cos 21^0

Prove that: cos 20^0cos 100^0+cos 100^0cos 140^0-\ cos 140^0cos 200^0=-3/4

Prove that: cos 80^0+cos 40^0-cos 20^0=0

Prove that: cos 80^0+cos 40^0-cos 20^0=0

Prove that: \ cos7^0cos 14^0cos 28^0cos 56^0=(sin 68^0)/(16cos83^0)

The expression (sin 22^0cos8^0+cos 158^0cos98^0)/(sin 23^0cos7^0+cos 157^0cos 97^0\ ) when simplified reduces to a. 1 b. -1 c. 2 d. none

Prove that: cos 100^0+cos 20^0=cos 40^0

if a=cos 0 + i sin 0,=cos 20 -i sin 20, c= cos3 0 + I sin 3 0 and if |{:(a,,b,,c),(b,,c,,a),(c,,a,,b):}| =0 then

Prove that: cos 55^0+cos 65^0+cos 175^0=0