\[- 2x^{2} - 3x + a\]
\[D = 9 + 8a\]
\[9 + 8a \geq 0\]
\[8a \geq - 9\]
\[a \geq - 1\frac{1}{8}\]
\[Ответ:\ \left\lbrack - 1\frac{1}{8}; + \infty \right).\]