[tex] \bf \sqrt{720x^2y^3}~~
\begin{cases}
720=2\cdot 2\cdot 2\cdot 2\cdot 3\cdot 3\cdot 5\\
\qquad 2^2\cdot 2^2\cdot 3^2\cdot 5\\
\qquad (2^2)^2\cdot 3^2\cdot 5\\
\qquad 4^2\cdot 3^2\cdot 5\\
\qquad (4\cdot 3)^2\cdot 5\\
\qquad 12^2\cdot 5\\
y^3=y^{2+1}\\
\qquad y^2y
\end{cases}\implies
\begin{array}{llll}
\sqrt{12^2\cdot 5x^2y^2y}
\\\\\\
12xy\sqrt{5y}
\end{array} [/tex]
