\begin{equation}x^{2}=81\end{equation}

\begin{equation}9x^{2}-900=0\end{equation}

\begin{equation}9x^{2}=576\end{equation}

\begin{equation}10(x-2)(x-6)=0\end{equation}

\begin{equation}\frac{1}{x+6}=\frac{x^{2}}{x^{2}-36}-(\frac{1}{x-6})\end{equation}

\begin{equation}\frac{1}{3} \times (x+8)(x-8)=0\end{equation}