`a) E(x) = -4x^3 + 5x -3/4 + x^3 - 2x^4`
` = 2x^4 - 3x^3 + 5x - 3/4`
`F(x) = 3x^2 - 9/4 -2x^3 + 6x -x^4`
` = -x^4 - 2x^3 + 3x^2 + 6x - 9/4`
`b) E(x) + F(x) = (2x^4 - 3x^3 + 5x - 3/4) + (-x^4 - 2x^3 + 3x^2 + 6x - 9/4)`
` = 2x^4 - 3x^3 + 5x - 3/4 - x^4 - 2x^3 + 3x^2 + 6x - 9/4`
` = (2x^4 - x^4) - (3x^3 + 2x^3) + 3x^2 + (5x +6x) - (3/4 + 9/4)`
` = x^4 - 5x^3 + 3x^2 + 11x - 3`
Vậy `E(x) + F(x) = x^4 - 5x^3 + 3x^2 + 11x - 3`
`b) F(x) - E(x) =(-x^4 - 2x^3 + 3x^2 + 6x - 9/4)-(2x^4 - 3x^3 + 5x - 3/4)`
` = -x^4- 2x^3 + 3x^2 + 6x-9/4-2x^4 + 3x^3 - 5x + 3/4`
` = (-x^4-2x^4) + (-2x^3 + 3x^3) + 3x^2 + (6x-5x) - (9/4 - 3/4)`
` = -3x^4 + x^3 + 3x^2 + x - 3/2`
Vậy `F(x) - E(x) = -3x^4 + x^3 + 3x^2 + x - 3/2`
