Grazie.
= SIN(α/2)/COS(α/2) - SIN(α)/COS(α/2)^2 =
=(SIN(α/2)·COS(α/2) - SIN(α))/COS(α/2)^2 =
=(- 1/2·SIN(α))/COS(α/2)^2=
essendo: COS(α/2)^2 = (1 + COS(α))/2 si ha:
=(- 1/2·SIN(α))/((1 + COS(α))/2)=
=(- SIN(α))/(1 + COS(α))
[sin(a/2)/cos(a/2) * cos^2(a/2) - sin a]/ cos^2(a/2) =
= (sin (a/2) cos (a/2) - sin a) : [ (1 + cos a)/2 ] =
= (2 * 1/2 sin a - 2 sin a ) / ( 1 + cos a ) =
= - sin a/(1 + cos a)