[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)\\\\
-------------------------------\\\\
5v^2-125=0\qquad \boxed{125=5^3=5\cdot 5^2}\qquad 5v^2-5(5^2)=0
\\\\\\
5(v^2-5^2)=0\implies v^2-5^2=0\implies (v-5)(v+5)=0
\\\\\\
v=
\begin{cases}
5\\
-5
\end{cases}[/tex]
