Помогите. номер 14. Нужно найти значения только косинуса

1) cos300° =cos(360° -60°) =cos60° = 1/2.2) cos(-690°) =cos690° =cos(2*360° -30°) =cos30° =√3/2.3)cos5π/6 =cos(π -π/6) = - cosπ/6 = -√3/2.4) cos(-3π/4) =cos3π/4 =cos(π -3π/4) = - cosπ/4 = -√2/2.