सिद्ध करें की `cos 55^@ * cos 35^@ = 1/2 cos 20^@`.

Prove that : cos 24^@+ cos 55^@ + cos 125^@ + cos204^@ + cos 300^@= 1/2 .

1 + cos 10^(@) + cos 20^(@) + cos30^(@) =

Prove that cos20^@cos 40^@=1/2(1/2+cos 20^@)

Evaluate : (sin 35^(@) cos 55^(@) + cos 35^(@) sin 55^(@))/ (cosec^(2) 10^(@) - tan^(2) 80^(@))

Evaluate: sin 35^(@) cdot sin 55^(@) - cos 35^(@) cdot cos 55^(@).

Prove that cos24^(@) + cos 55^(@) + cos125^(@) +cos204^(@) + cos300^(@) = 1/2

The smallest positive value of x (in degrees) for whichcos tanx=(cos5^@ cos 20^@ + cos 35^@ cos 50^@-sin 50^@ sin 20^@ - sin35^@ sin50^@)/(sin5^@ cos 20^@ - sin 35^@ cos 50^@ + cos 5^@ sin 20^@ - cos 35^@ sin 50^@) is equal to