3. Используя свойства четности и периодичности функций y = sinx, y = cosx, найдите значение выражения cos(19π/6) + sin(-21π/4).

cos(19π/6) = cos(3π + π/6) = cos(π + π/6) = -cos(π/6) = -√3/2

sin(-21π/4) = -sin(21π/4) = -sin(5π + π/4) = -sin(π + π/4) = sin(π/4) = √2/2

cos(19π/6) + sin(-21π/4) = -√3/2 + √2/2 = (√2 - √3)/2

Ответ: (√2 - √3)/2