4.12 sin(π – α)ctg(3π/2 + α) / (tg(2π – α)cos(π/2 + α))

sin(π - α) = sin(α); ctg(3π/2 + α) = -tg(α); tg(2π - α) = -tg(α); cos(π/2 + α) = -sin(α). (sin(α) * (-tg(α))) / ((-tg(α)) * (-sin(α))) = (-sin(α) * tg(α)) / (tg(α) * sin(α)) = -1