Question

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)

Answer 1

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

Answer 2

已知A=x3-23x2y+2xy-22y3 B=x3+3x2y-5xy2-y3 C=-2x3+22x2y-5xy2+3y3 求（1）A+(B-C)
B-C
= x3+3x2y-5xy2-y3-(-2x3+22x2y-5xy2+3y3)
= x3+3x2y-5xy2-y3+2x3-4x2y+5xy2-3y3
=3X3-X2Y-4Y3
A+(B-C)
= x3-23x2y+2xy-22y3+3X3-X2Y-4Y3
= x3-8x2y+2xy-4y3+3X3-X2Y-4Y3
=4 x3-9 x2y+2xy-8y3
(2)A-(B-C)
= x3-23x2y+2xy-22y3-(3X3-X2Y-4Y3)
= x3-8x2y+2xy-4y3-3X3+X2Y+4Y3
=-2 x3-7 x2y+2xy

Answer 3

亲，自己要认真哟！
化简就行了哦！
努力啊！

追问

怎么做？教一下