\ANG{
Geben Sie ${\DD}_f$ an und berechnen Sie alle Grenzwerte an den R"andern von
${\DD}_f$:\\[2mm]
(a)\quad $\D f(x) = \frac{x^2}{9-x^2}$\quad ; ${\DD}_f$ maximal\qquad
(b)\quad $\D f(x) = \frac{x}{9-x^2}$\quad ; ${\DD}_f$ maximal
}
\LSG{
  \begin{enumerate}
  \item  $\DD_{f}=\RR\backslash \{\pm 3\}$,\quad 
    $\D\lim_{x\to 3^{\pm}}f(x)=\mp\infty$,\quad 
    $\D\lim_{x\to (-3)^{\pm}}f(x)=\pm\infty$\\[2mm]
    $\D\lim_{x\to\infty}f(x)=(-1)^{-}$
  \item $\DD_{f}=\RR\backslash \{\pm 3\}$,\quad 
    $\D\lim_{x\to 3^{\pm}}f(x)=\mp\infty$,\quad 
    $\D\lim_{x\to (-3)^{\pm}}f(x)=\mp\infty$\\[2mm]
    $\D\lim_{x\to\infty}f(x)=0^{\mp}$
  \end{enumerate}
}