Đáp án đúng: C
Giải chi tiết:Thu gọn:
\(\begin{array}{l}A\left( x \right) = {x^2} + 5{x^4} - 3{x^3} + {x^2} - 4{x^4} + 3{x^3} - x + 5\\\,\,\,\,\,\,\,\,\,\,\,\, = \left( {5{x^4} - 4{x^4}} \right) + \left( {3{x^3} - 3{x^3}} \right) + \left( {{x^2} + {x^2}} \right) - x + 5\\\,\,\,\,\,\,\,\,\,\,\,\, = {x^4} + 2{x^2} - x + 5\\B\left( x \right) = x - 5{x^3} - {x^2} - {x^4} + 5{x^3} - {x^2} + 3x - 1\\\,\,\,\,\,\,\,\,\,\,\,\, = - {x^4} + \left( {5{x^3} - 5{x^3}} \right) + \left( { - {x^2} - {x^2}} \right) + \left( {x + 3x} \right) - 1\\\,\,\,\,\,\,\,\,\,\,\,\, = \, - {x^4} - 2{x^2} + 4x - 1\end{array}\)
Vậy \(A\left( x \right)\, = {x^4} + 2{x^2} - x + 5;\,\,B\left( x \right) = \, - {x^4} - 2{x^2} + 4x - 1\)
Chọn C