Ta có: \(\sqrt{\frac{64}{81}}\cdot\left(x-1\right)^2=-\frac{1}{3}\)
\(\Leftrightarrow\frac{8}{9}\cdot\left(x-1\right)^2=\frac{-1}{3}\)
\(\Leftrightarrow\left(x-1\right)^2=-\frac{1}{3}:\frac{8}{9}=\frac{-1}{3}\cdot\frac{9}{8}=\frac{-9}{24}=\frac{-3}{8}\)(vô lý vì \(\left(x-1\right)^2\ge0\forall x\))
Vậy: \(S=\varnothing\)