4.9 sin (π - α) + cos (π/2 + α) - tg(π/2 + α) + ctg (π + α)

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