\[2x^{2} + 24xy + 72y^{2} =\]
\[= 2 \cdot \left( x^{2} + 12xy + 36y^{2} \right) =\]
\[= 2 \cdot (x + 6y)^{2} =\]
\[= 2 \cdot (x + 6y)(x + 6y)\]