\[36a² + 8ab + b²\]
\[36a^{2} + 12ab + b^{2} = (6a + b)^{2}\]
\[16a^{2} + 8ab + b^{2} = (4a + b)^{2}\ \]
\[36a^{2} + 8ab + \frac{4}{9}b^{2} = \left( 6a + \frac{2}{3}b \right)^{2}.\]