сtg(x/3)`=-1/sin^2(x/3)*(1/3)=-1/(3sin^2(x/3)=
подставлю x=pi; sin(pi/3)=√3/2
=-1(3(√3/2)^2)=-1/(3*3/4)=-4/9
сtg(x/3)`=-1/sin^2(x/3)*(1/3)=-1/(3sin^2(x/3)=
подставлю x=pi; sin(pi/3)=√3/2
=-1(3(√3/2)^2)=-1/(3*3/4)=-4/9