COS(6·pi - α)·SEC(α - 6·pi)=
=COS(α)·(1/COS(α))= 1
------------------------
COS(α - pi/2)·COS(3/2·pi - α)=
=SIN(α)·(- SIN(α))= - SIN(α)^2
-------------------------
COT(4·pi - α)·TAN(3/2·pi - α)=
=(- COT(α))·COT(α)= - COT(α)^2
---------------------------
COS(5·pi + α)·SIN(3/2·pi + α)=
=(- COS(α))·(- COS(α)) = COS(α)^2
Quindi:
1/(- SIN(α)^2) + (- COT(α)^2)/COS(α)^2=
=1/(- SIN(α)^2) + (- 1/SIN(α)^2)=
=- 2/SIN(α)^2