\[\left\{ \begin{matrix} 4 - a^{2} < 0 \\ D \leq 0\ \ \ \ \ \ \ \ \\ \end{matrix} \right.\ \text{\ \ \ \ \ \ \ \ \ \ \ \ \ \ }\]
\[\left\{ \begin{matrix} a² > 4\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \\ 4a² - 16a + 16 - 16 + 4a^{2} \leq 0 \\ \end{matrix} \right.\ \]
\[8a^{2} - 16a \leq 0\]
\[8a(a - 2) \leq 0\]
\[a(a - 2) \leq 0\]
\[0 \leq a \leq 2.\]
\[Ветви\ параболы\ направлены\ \]
\[вниз:\]
\[4 - a^{2} < 0\]
\[a^{2} - 4 > 0\]
\[(a + 2)(a - 2) > 0\]
\[a < - 2;\ \ a > 2.\]
\[Ответ:\ a \in \varnothing.\]