1.3x+2xy-4y²-3xy-4y²-3x²=0
-3x²-8y²-xy+3x=0
3x²+8y²+xy-3x=0.
2.原式=3x³-x³-6x²+7x-2x³+6x²+8x
=-x³+15x.
3.原式=3x²-4y²-x²+2xy+y²+3x²-xy-y²
=5x²-5y²+xy.
4.请楼主把题目改一下,不应该是(x=2)²+|y=1|=0吧,楼主改了我就来改回答.
5.将A、B分别代入,得:
(3m²-m+1)-(2m²-m-7)+C=0
3m²-m+1-2m²+m+7=-C
m²+8=-C
C=-m²-8.