\[81x^{2} - 36x + 4 = 0\]
\[(9x - 2)^{2} = 0\]
\[9x - 2 = 0\]
\[9x = 2\]
\[x = \frac{2}{9}\]
\[Ответ:x = \frac{2}{9}\text{.\ }\]