Tính \(A\left( x \right) - B\left( x \right).\)

* Hướng dẫn giải

\(\begin{array}{l}\,A\left( x \right) - B\left( x \right) = 3{x^3} + 3{x^2} + 2x - 1 - \left( {3{x^3} - 2{x^2} + x + 4} \right)\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 3{x^3} + 3{x^2} + 2x - 1 - 3{x^3} + 2{x^2} - x - 4\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = \left( {3{x^3} - 3{x^3}} \right) + \left( {3{x^2} + 2{x^2}} \right) + \left( {2x - x} \right) + \left( { - 1 - 4} \right)\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 5{x^2} + x - 5\end{array}\)

Chọn C