k=lim (x->+-00) [(x^3+1)^(1/3)+(x^3-1)^(1/3)]/x=
=lim (x->+-00) [(x^3*(1+1/x^3))^(1/3)+(x^3*(1-1/x^3))^(1/3)]/x=
=lim (x->+-00) [x*((1+1/x^3)^(1/3)+(1-1/x^3)^(1/3))]/x=
=lim (x->+-00) (1+1/x^3)^(1/3)+(1-1/x^3)^(1/3)=2

Теперь найдите b=lim (x->+-00) [y(x)-kx]