ctg(π/2+α) • tg(3π/2+α) - sin(π+α) • cos(π/2+α) =
-tgα • (-ctgα) - (-sinα) • (-sinα) = 1 - sin²α =
= cos²α
ctg(π/2+α) • tg(3π/2+α) - sin(π+α) • cos(π/2+α) =
-tgα • (-ctgα) - (-sinα) • (-sinα) = 1 - sin²α =
= cos²α