f(x)=20-12x-0,4x^2.
\[f(x) = 20 - 12x - 0,4x^{2} \Longrightarrow \ \]
\[\Longrightarrow ветви\ вниз\]
\[x_{0} = \frac{12}{- 0,8} = - 15\]
\[y_{0} = 20 + 180 - 90 = 110 \Longrightarrow\]
\[\Longrightarrow ( - 15;110).\]
\[E(f) = ( - \infty;110).\]
\[возрастает\ на\ ( - \infty;\ - 15)\]
\[убывает\ на\ ( - 15;\ + \infty).\]