\[y = - 2x^{2} - 4x + 6\]
\[x_{b} = - \frac{b}{2a} = \frac{4}{- 4} = - 1\]
\[y_{b} = - 2 + 4 + 6 = 8\]
\[y > 0\ \ \ при\ \ x \in ( - 3;1).\]