\[\text{A\ }(a;27):\ \ \ \ \ \]
\[y = 3x^{2}\]
\[27 = 3a^{2}\text{\ \ \ }\]
\[a^{2} = 9\ \ \ \ \]
\[a = \pm 3\]
\[Ответ:\ \ при\ a = \pm 3.\]