Пожалуйста, докажите
cos36-cos72=1/2
cos 36° - cos 72° = 1/2
=> cos 36° - (2 cos^2(36°) - 1) = 1/2
=> cos 36° - 2 cos^2(36°) + 1 = 1/2
=> 4 cos^2(36°) - 2 cos 36° - 1 = 0