a) `P(x) + Q(x) = x^3 - 6x + 2 + 2x^2 - 4x^3 + x -5`
`= (x^3 - 4x^3) - (6x -x ) + (2 -5) + 2x^2`
`= -3x^3 - 5x - 3 + 2x^2`
Vậy `P(x) + Q(x) = -3x^3 - 5x -3 + 2x^2`
$\\$
b) `P(x) - Q(x) = (x^3 - 6x + 2) - ( 2x^2 - 4x^3 + x -5)`
`= x^3 -6x + 2 - 2x^2 + 4x^3 - x + 5`
`= (x^3 + 4x^3) - (6x + x)+ (2+5) -2x^2`
`= 5x^3 - 7x + 7 - 2x^2`
Vậy `P(x) - Q(x) = 5x^3 - 7x + 7 - 2x^2`