[tex]\bf \qquad \textit{parabola vertex form}\\\\
\begin{array}{llll}
y=a(x-{{ h}})^2+{{ k}}\\\\
x=a(y-{{ k}})^2+{{ h}}
\end{array} \qquad\qquad vertex\ ({{ h}},{{ k}})\\\\
-------------------------------\\\\
y=-(x-\stackrel{h}{2})^2\stackrel{k}{-1}\qquad \qquad \stackrel{vertex~(h,k)}{(2,-1)}[/tex]
