\[49a² - 8ab + b²\]
\[49a^{2} - 14ab + b^{2} = (7a - b)^{2}\]
\[16a^{2} - 8ab + b^{2} = (4a - b)^{2}\]
\[49a^{2} - 8ab + \frac{196}{64}b^{2} =\]
\[= \left( 7a - \frac{7}{4}b \right)^{2}.\]