\[\boxed{\text{842\ (842).\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[= \left( 4a^{2} + 3 + \left( 7 - 4a^{2} \right) \right)^{2} =\]
\[= \left( 4a^{2} + 3 + 7 - 4a^{2} \right)^{2} = 10^{2} =\]
\[= 100\]
\[100 = 100 \Longrightarrow ч.т.д.\]
\[= (a - 3b)^{2}(a + 3b)^{2} =\]
\[= \left( a^{2} - 9b^{2} \right)^{2} - \left( a^{2} - 9b^{2} \right)^{2} =\]
\[= 0\]
\[0 = 0 \Longrightarrow ч.\ т.\ д.\]