[tex]\bf \textit{difference of squares}
\\ \quad \\
(a-b)(a+b) = a^2-b^2\qquad \qquad
a^2-b^2 = (a-b)(a+b)\\\\
-------------------------------\\\\
9x^2-5\qquad
\begin{cases}
9x^2=3^2x^2\\
\qquad (3x)^2\\
5=\sqrt{5^2}\\
\qquad (\sqrt{5})^2
\end{cases}\implies
\begin{array}{llll}
(3x)^2-(\sqrt{5})^2
\\\\\\
(3x-\sqrt{5})~(3x+\sqrt{5})
\end{array}[/tex]
