u=arctg(2x-1)
y`=3u^2*u`
y`=(3arctg^2(2x-1)) * (arctg(2x-1))`=
=(3arctg^2(2x-1))* (1/(1+(2x-1)^2)*(2x-1)`=
=(3arctg^2(2x-1)) * (1/(1+(2x-1)^2)*(2)=
=(6arctg^2(2x-1) )* (1/(1+(2x-1)^2)=
=(6arctg^2(2x-1)) / (1+4x^2-4x+1)=
=(6arctg^2(2x-1)) / (4x^2-4x+2)=
[b]=(3arctg^2(2x-1) )/ (2x^2-2x+1)[/b]