已知a=x^3-2^3x^2y+2xy-2-^2y^3 B=x^3+3x^2y-5xy^2-y^3 C=-2x^3+2^

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已知a=x^3-2^3x^2y+2xy-2-^2y^3 B=x^3+3x^2y-5xy^2-y^3 C=-2x^3+2^2x^2y-5xy^2+3y^3 求（1）A+(B-C)
（2）A-(B-C)

A=x^3-2^3x^2y+2xy-2-^2y^3
B=x^3+3x^2y-5xy^2-y^3
C=-2x^3+2^2x^2y-5xy^2+3y^3
B-C
=x^3+3x^2y-5xy^2-y^3 -(-2x^3+2^2x^2y-5xy^2+3y^3)
=x^3+3x^2y-5xy^2-y^3+2x^3-2^2x^2y+5xy^2-3y^3
=x^3+2x^3+3x^2y-2^2x^2y-5xy^2+5xy^2-3y^3-y^3
=3x^3+3x^2y-4x^2y-4y^3
=3x^3-x^2y-4y^3
A+(B-C)
=x^3-2^3x^2y+2xy-2^2y^3+3x^3-x^2y-4y^3
=x^3-8x^2y+2xy-4y^3+3x^3-x^2y-4y^3
=x^3+3x^3-8x^2y-x^2y+2xy-4y^3-4y^3
=4x^3-9x^2y+2xy-8y^3
A-(B-C)
=x^3-2^3x^2y+2xy-2^2y^3-(3x^3-x^2y-4y^3)
=x^3-8x^2y+2xy-4y^3-3x^3+x^2y+4y^3
=x^3-3x^3-8x^2y+x^2y+2xy-4y^3+4y^3
=-2x^3-7x^2y+2xy

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