да я допустила

int dy/siny=
=int((2dt/(1+t^2))/(2t/(t^2+1)))=
=int((2dt/(1+t^2)) : (2t/(t^2+1)))=
=int((2dt/(1+t^2)) * ((t^2+1)/2t))=
=int(dt/t)=
=int(dt/t)=
=ln(t)+c=
=ln(tg(y/2))+c