Answer :

konrad509
[tex]a>0 \Rightarrow \hbox{no maximum}[/tex]

[tex]y_{min}=\frac{-b^2+4ac}{4a}\\y_{min}=\frac{-0^2+4\cdot1\cdot9}{4\cdot1}\\ y_{min}=9[/tex]
kate200468
[tex]f(x)= x^2+9\\\\for\ each\ x\in R\\\\x^2 \geq 0\ \ \ \Rightarrow\ \ \ x^2+9 \geq 9\ \ \ \Rightarrow\ \ \ f(x) \geq 9\\\\y_{min}=9\\ y_{max}\ \ \ \rightarrow\ \ \ not\ exist[/tex]