\[f(x) = 6x - 2x^{2} \Longrightarrow ветви\ вниз,\ \]
\[x_{0} = \frac{- 6}{- 4} = 1,5,\ \ \]
\[y_{0} = 9 - 4,5 = 4,5 \Longrightarrow \ \ \ (1,5;4,5)\]
\[E(f) = ( - \infty;4,5\rbrack.\]