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Đáp án:

`a)`

`@A(x)=-2x^3+3x+4x^2+5x^5+6-4x^4`

    `A(x)=5x^5-4x^4-2x^3+4x^2+3x+6`

~~~~~~~~~~~~~~~~~

`@B(x)=2x^4-x+3x^2-2x^3+4-x^5`

    `B(x)=-x^5+2x^4-2x^3+3x^2-x+4`

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`b)`

`*** A(x)+B(x)=(5x^5-4x^4-2x^3+4x^2+3x+6)+(-x^5+2x^4-2x^3+3x^2-x+4)`

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

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

`=4x^5-2x^4-4x^3+7x^2+2x+10`

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`*** A(x)-B(x)=(5x^5-4x^4-2x^3+4x^2+3x+6)-(-x^5+2x^4-2x^3+3x^2-x+4)`

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

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

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

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