Rút gọn các biểu thức sau: c) ( 3 x − 1 ) ^2 + 2 ( 1 − 3 x ) ( 4 + 3 x ) + ( 3 x + 4 ) ^2 .

c) \({\left( {3x - 1} \right)^2} + 2\left( {1 - 3x} \right)\left( {4 + 3x} \right) + {\left( {3x + 4} \right)^2}\)

\( = {\left( {1 - 3x} \right)^2} + 2\left( {1 - 3x} \right)\left( {3x + 4} \right) + {\left( {3x + 4} \right)^2}\)

\( = {\left( {1 - 3x + 3x + 4} \right)^2}\)

\( = {5^2} = 25.\)