\[\boxed{\text{838.}\text{\ }еуроки - ответы\ на\ пятёрку}\]
\[\textbf{а)}\ 5 \cdot (3a + 7)^{2} = 5 \cdot \left( 9a^{2} + 42a + 49 \right) = 45a² + 210a + 245\]
\[\textbf{б)} - 6 \cdot (4 - b)^{2} = - 6 \cdot \left( 16 - 8b + b^{2} \right) = - 6b^{2} + 48b - 96\]
\[\textbf{в)} - 3 \cdot (2 - x)^{2} - 10x = - 3 \cdot \left( 4 - 4x + x^{2} \right) - 10x =\]
\[= - 12 + 12x - 3x^{2} - 10x = - 3x^{2} + 2x - 12\]
\[\textbf{г)}\ 12a² - 4 \cdot (1 - 2a)^{2} + 8 = 12a^{2} - 4 \cdot \left( 1 - 4a + 4a^{2} \right) + 8 =\]
\[= 12a² - 4 + 16a - 16a^{2} + 8 = - 4a^{2} + 16a + 4\]