Sinus, kosinus, tangens va kotangens ta’riflari

P(1; 0) nuqtani α burchakka burishda hosil bo‘lgan nuqtaning ordinatasi α burchakning sinusi (sin α), abssissasi esa kosinusi (cos α) deyiladi. Tangens tg α = sin α : cos α (cos α ≠ 0, ya’ni α ≠ π/2 + πk), kotangens ctg α = cos α : sin α (sin α ≠ 0, ya’ni α ≠ πk). Birlik aylana nuqtasining koordinatalari −1 dan 1 gacha bo‘lgani uchun −1 ≤ sin α ≤ 1 va −1 ≤ cos α ≤ 1. Asosiy qiymatlar: sin 0 = 0, sin π/6 = 1/2, sin π/4 = √2/2, sin π/3 = √3/2, sin π/2 = 1; cos esa teskari tartibda: 1, √3/2, √2/2, 1/2, 0. tg π/6 = √3/3, tg π/4 = 1, tg π/3 = √3. Eng sodda tenglamalar: sin t = 0 da t = πk; cos t = 0 da t = π/2 + πk; sin t = 1 da t = π/2 + 2πk; cos t = 1 da t = 2πk (k ∈ Z).