Đáp án:
$\begin{array}{l}
b)A\left( x \right) = 6{x^3} - 2{x^2} + 4x + 7\\
B\left( x \right) = 4{x^3} + {x^2} + 3x + 3\\
A\left( x \right) + B\left( x \right)\\
= 6{x^3} - 2{x^2} + 4x + 7 + 4{x^3} + {x^2} + 3x + 3\\
= 10{x^3} - {x^2} + 7x + 10\\
A\left( x \right) - B\left( x \right)\\
= 6{x^3} - 2{x^2} + 4x + 7 - \left( {4{x^3} + {x^2} + 3x + 3} \right)\\
= 6{x^3} - 4{x^3} - 2{x^2} - {x^2} + 4x - 3x + 7 - 3\\
= 2{x^3} - 3{x^2} + x + 4
\end{array}$
