1) 5(sin²α + cos²α) - 4ctgα = 5 - 4/tgα
при tgα = 2, получаем:
5 - 4/2 = 3
2) 7cos(π + β) - 2sin(π/2 + β) = - 7сosβ - 2cosβ = - 9cosβ
при cosβ = - 1/3 получаем:
-9*(-1/3) = 3
3) (sin2α - cos2α)/(sin2α + cos2α) = (делим на cos2α ≠ 0
(tg2α - 1) / (tg2α + 1) = [2tgα/(1 - tg²α) - 1] / [2tgα/(1 - tg²α) + 1]
при tgα = 1/2 получим:
[2*0,5 / (1 - 1/4) - 1] / [2*0,5 / (1 - 1/4) + 1] =
= (4/3 - 1) / (4/3 + 1) = (1/3) : (7/3) = 1/7