Используя свойство периодичности функции /(x) = cos x, найдите: a) cos 13pi/6 6) cos 19pi/3 B) cos 33pi/4 г) cos11pi

Используем периодичность косинуса: cos(x + 2πk) = cos x.

• a) cos(13π/6) = cos(2π + π/6) = cos(π/6) = √3/2
• b) cos(19π/3) = cos(6π + π/3) = cos(π/3) = 1/2
• c) cos(33π/4) = cos(8π/4 × 1 + π/4) = cos(2π + π/4) = cos(π/4) = √2/2
• d) cos(11π) = cos(11π − 10π) = cos(π) = −1

Ответы: √3/2, 1/2, √2/2, −1.