[tex]\it f(x) = x^2+9x+20 = x^2+5x+4x+20 = x(x+5) +4(x+5) =
\\ \\
= (x+5)(x+4)
\\ \\
f(x) =0 \Rightarrow (x+5)(x+4) =0 \Rightarrow \begin{cases} \it x_1 = -5
\\ \\
\it x_2 = -4\end{cases}[/tex]
[tex]\it f(x) \leq 0 \ pentru\ x \in [-5,\ -4]
\\ \\
f(x) \ \textgreater \ 0\ pentru\ x \in \mathbb{R} \backslash [-5,\ -4][/tex]
