Răspuns:
cos 45° + cos130°=
= 2*cos (45°+130°/2) * cos(45°-130°/2)
= 2*cos( 175°/2) *cos(-85°/2)
= 2*cos( (180°-5°)/2) * cos (85°/2)
= 2*cos( 90°- 5°/2) * cos (85°/2)
= 2* sin (5°/2) * cos (85°/2)
