`2A`

Cách `1`

`a)(3x^3 - 5x^2 + 6x+5) - (x^3 - x^2 + 4x -1)`

`=3x^3 - 5x^2 + 6x + 5 - x^3 + x^2 - 4x +1`

`=2x^3 + 4x^2 + 2x + 6`

`b)(5x^3 - 2x^2 + x -3) - ( 4x^3 + 5x -1)`

`=5x^3 - 2x^2 + x -3 - 4x^3 - 5x +1`

`=x^3 - 2x^2 - 4x -2`

`c)(x^4 + 3x^2 +5) - ( x^4 - x^3 + 2x^2 + 4x +1)`

`=x^4 + 3x^2 + 5 - x^4 + x^3 - 2x^2 - 4x -1`

`=x^3 + x^2 - 4x +4`

`d)(14x^3 + 2x^2 + 7x ) - (11x^3 + x^2 + 5x -4)`

`=14x^3 + 2x^2 + 7x - 11x^3 - x^2 - 5x +4`

`=3x^3 + x^2 + 2x +4`

Cách `2`

       `3x^3 - 5x^2 + 6x+5`

`-`

        `x^3 - x^2 + 4x -1`

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       `2x^3 + 4x^2 + 2x + 6`

``

       `5x^3 - 2x^2 + x -3`

`-` 

       `4x^3`           `+ 5x -1`

______________________________

       `x^3 - 2x^2 - 4x -2`

``

       `x^4`     ` + 3x^2 +5`

`-`

      ` x^4 - x^3 + 2x^2 + 4x +1`

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       `x^3 + x^2 - 4x +4`

``

     `14x^3 + 2x^2 + 7x`

`-`

      `11x^3 + x^2 + 5x -4`

______________________________

      `3x^3 + x^2 + 2x +4`