Tổng P(x) + Q(x) là.

Chọn C

Ta có: \(P\left( x \right) + Q\left( x \right) = 5{x^3} + {x^2} - x + 5 + {x^3} - 2{x^2} + 3x + 2\)

                                \( = 5{x^3} + {x^3} + {x^2} - 2{x^2} + 3x - x + 5 + 2\)

                                \( = \left( {5{x^3} + {x^3}} \right) + \left( {{x^2} - 2{x^2}} \right) + \left( {3x - x} \right) + 5 + 2\)

                                \( = 6{x^3} - {x^2} + 2x + 7\).