a) `P(x) = 5x^3 + 3x - 4x^4 - 2 + 4x^2 -6`
`P(x) = 5x^3 + 4x - 4x^4 - (2+6) + 4x^2`
`P(x) = 5x^3 + 4x - 4x^4 - 8 + 4x^2`
Sắp xếp: `P(x) = -4x^4 + 5x^3 + 4x^2 + 4x -8`
`Q(x) = 2x^4 - x + 3x^2 - 2x^3 + 1/4 - x^5`
Sắp xếp: `Q(x) = -x^5 + 2x^4 - 2x^3 + 3x^2 -x + 1/4`
b) `A(x) + Q(x) =P(x)`
`=> A(x)= P(x)-Q(x)`
`= (-4x^4 + 5x^3 + 4x^2 + 4x-8) - (-x^5 + 2x^4 - 2x^3 + 3x^2 -x + 1/4)`
`= -4x^4 + 5x^3 + 4x^2 + 4x -8 + x^5 - 2x^4 + 2x^3 - 3x^2 + x - 1/4`
`= (-4x^4 - 2x^4) + (5x^3 + 2x^3) + (4x^2 - 3x^2) + (4x +x) + x^5 - (8 +1/4)`
`= -6x^4 + 7x^3 + x^2 + 5x + x^5 - 33/4`
Vậy `A(x) = -6x^4 + 7x^3 + x^2 + 5x + x^5 - 33/4`