x/a-1=y
x/a=y+1
tg((Pi/2)( y+1))=tg(Pi/2+ Pi*y/2)= -ctg (Pi*y/2)
lim=e^(-ctg (Pi*y/2)*ln(1-y))=e^((ln(1-y))/ tg (Pi*y/2))
ln(1-y)=-y
tg (Pi*y/2)= Pi*y/2
Lim=e^lim-y/ (Pi*y/2)=e^-2/Pi
Ответ: e^-2/Pi
Так???