\[\boxed{\text{731.}\text{\ }\text{еуроки}\text{-}\text{ответы}\text{\ }\text{на}\text{\ }\text{пятёрку}}\]
\[\textbf{а)}\ 4x^{2} - 12x + 9 = (2x - 3)^{2}\]
\[\textbf{б)}\ 1 - 14a + 49a^{2} = (1 - 7a)^{2}\]
\[\textbf{в)}\ 25 + 4c^{2} + 20c =\]
\[= 4c^{2} + 20c + 25 = (2c + 5)^{2}\]