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

\begin{equation}7x^{2}-63=0\end{equation}

\begin{equation}10x^{2}=640\end{equation}

\begin{equation}3(x-5)(x-6)=0\end{equation}

\begin{equation}\frac{1}{x+3}=\frac{x^{2}}{x^{2}-9}-(\frac{1}{x-3})\end{equation}

\begin{equation}\frac{1}{9} \times (x+8)(x-8)=0\end{equation}