Davriy jarayonlar, sinus va kosinus

Radiusi 1 bo‘lgan aylanada (1; 0) nuqtani koordinatalar boshi atrofida α burchakka burishdan hosil bo‘lgan nuqtaning ordinatasi sin α, abssissasi cos α deyiladi. Nuqta aylanada yotgani uchun sin²α + cos²α = 1 (asosiy trigonometrik ayniyat). Burchak radianda ham o‘lchanadi: 180° = π rad, shuning uchun α° = α · π/180 radian; masalan, 30° = π/6, 45° = π/4, 60° = π/3, 90° = π/2. Maxsus qiymatlar: sin 30° = 1/2, cos 30° = √3/2, sin 45° = cos 45° = √2/2, sin 60° = √3/2, cos 60° = 1/2; sin 90° = 1, cos 90° = 0. Ikkinchi chorakda sin(180° − α) = sin α, cos(180° − α) = −cos α, chunki nuqtalar Oy o‘qiga nisbatan simmetrik. y = sin x va y = cos x ning davri 2π, amplitudasi 1, qiymatlari [−1; 1] oraliqda. y = a sin bx + c funksiyaning amplitudasi |a|, davri 2π/|b|, bosh o‘qi y = c.