\[f(x) = 6x - 3x^{2} \Longrightarrow ветви\ вниз\]
\[x_{0} = \frac{- 6}{- 6} = 1;\ \ y_{0} = 3 \Longrightarrow (1;3)\]
\[\text{E\ }(f) = ( - \infty;3\rbrack\]