$\text{Đáp án:}$
$a)\text{Ta có:}$
$h(-1)=(-1)^3-13(-1)+9=(-1)+13+9=21$
$h(-2)=(-2)^3-13(-2)+9=(-8)+26+9=27$
$b)Để h(x)=9$
$⇔x^3-13x+9=9$
$⇔x^3-13x=0$
$⇔x(x^2-13)=0$
$⇔\left[ \begin{array}{l}x=0\\x^2-13=0\end{array} \right.$
$⇔\left[ \begin{array}{l}x=0\\x^2=13\end{array} \right.$
$⇔\left[ \begin{array}{l}x=0\\x=\sqrt{13}\\x=-\sqrt{13}\end{array} \right.$
