\[\boxed{\text{709\ (709).\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[1)\ 3a² + 6\text{ab} + 3b² =\]
\[= 3 \cdot \left( a^{2} + 2\text{ab} + b^{2} \right) =\]
\[= 3 \cdot (a + b)²\]
\[2)\ 5m² + 5n² - 10\text{mn} =\]
\[= 5 \cdot \left( m^{2} - 2mn + n^{2} \right) =\]
\[= 5 \cdot (m - n)²\]
\[3) - 3x^{2} + 12x - 12 =\]
\[= - 3 \cdot \left( x^{2} - 4x + 4 \right) =\]
\[= - 3 \cdot (x - 2)²\]
\[4) - 7b^{2} - 14bc - 7c^{2} =\]
\[= - 7 \cdot \left( b^{2} + 2bc + c^{2} \right) =\]
\[= - 7 \cdot (b + c)²\]
\[5)\ x²y + 14xy² + 49y³ =\]
\[= y\left( x^{2} + 14xy + 49y^{2} \right) =\]
\[= y(x + 7y)²\]
\[6) - 8a^{3}b + 56a^{2}b^{2} - 98ab^{3} =\]
\[= - 2ab\left( 4a^{2} - 28ab + 49b^{2} \right) =\]
\[= - 2ab(2a - 7b)²\]