Question

1、若A=3x^2y+4xy+x-7,B=x^2y+3xy-3x,且A-3B与x无关，求y与A-3B的值

2、若A=2x^2-5xy-3y^2,B=2x^2+3xy-4y^2,且2A-3B-C=0,求C

3、已知多项式A与x^2+2x-3相加得-2x^2-3x+3,求多项式A

Answer 1

你好，答案如下：
1、解：A-3B=(3x^2y+4xy+x-7)-3(x^2y+3xy-3x)
=3x^2y+4xy+x-7-3x^2y-9xy+9x
=-5xy+10x-7
y=2,A-3B=-7
2、解：C=2A-3B
=2(2x^2-5xy-3y^2)-3(2x^2+3xy-4y^2)
=4x^2-10xy-6y^2-6x^2-9xy+12y^2
=-2x^2-19xy+6y^2
3、解：A=-2x^2-3x+3-(x^2+2x-3)
=-2x^2-3x+3-x^2-2x+3
=-3x^2-5x+6