\[\ x^{2} - 36x + 324 = 0\]
\[D = b^{2} - 4ac = 1296 - 4 \cdot 1 \cdot 324 =\]
\[= 1296 - 1296 = 0\]
\[x = \frac{36}{- 72} = - \frac{1}{2}\]
\[Ответ:\ \ x = - \frac{1}{2}.\]