\[49x^{2} - 42x + 9 = 0\]
\[(7x - 3)^{2} = 0\]
\[7x - 3 = 0\]
\[7x = 3\]
\[x = \frac{3}{7}\]
\[Ответ:x = \frac{3}{7}\text{.\ }\]