已知A=2x^2 3xy-2x-1,B=-x^2 xy 1-搜答案-搜狗做题网

x-xy=8(1)xy-y=-9(2)则有(1)-(2):X-XY-XY+Y=X+Y-2XY=8-(-9)=17

A-2B=2x²+3xy+2y-1-2(x²-xy+x-1/2)=2x²+3xy+2y-1-2x²+2xy-2x+1=5xy-2x+2y=x(5y-2)+2y根

(1)A-B=2x^2-3xy+2y^2-(x^2+xy-3y^2)=2x^2-3xy+2y^2-x^2-xy+3y^2=x^2-4xy+5y^2(2)2A-3B+C=0即：2（2x^2-3xy+2y

A-2B=5x²-3xy²+2xy-2(7xy²-2xy+x²y)=5x²-3xy²+2xy-14xy²+4xy-2x²

X-a的绝对值+（y+4）的平方=0绝对值和平方都是非负值,只有他们同时为0时,和才为0所以x-a=0,y+4=0=>x=a,y=-4A-2B=2x^2-4xy+6y^2+3x-y-2x^2+4xy-

3A+6B=3(2x²+3xy-2x-1)+6(-x²+xy-1)=6x²+8xy-6x-3-6x²+6xy-6=((14y-6)x-9值与x无关则x系数为0所

（1）∵xy+x=-1①，xy-y=-2②，∴①-②得x+y=1；（2）先把xy+x=-1，xy-y=-2的值代入代数式，得原式=-x-[2y-1+3x]+2[x+4]=-x-2y+1-3x+2x+8

(1)x=y=-2时,A=2×(-2)^3+3×(-2)×(-2)+2×(-2)-1=-9,B=(-2)^2-(-2)×(-2)+(-2)-1/2=-5/2A-2B=-9+5=-4(2)A-2B=2x

答案是3/2你是不是把分母打错了教你个方法因为上下是齐次的直接令x=3y=2带入就行

解题思路：题不完整，请补充解题过程：.最终答案：略

2(x+xy)-[(xy-3y)-x]-(-xy)=2x+2xy-xy+3y+x+xy=3x+3y+2xy=3（x+y）+2xy=3*（-2）+2*3=0

a-2b=(5x²y-3xy²+4xy)-2(7xy²-2xy+x²y)=5x²y-3xy²+4xy-14xy²+4xy-2x&#

A+B=(x²-3xy+y²)+(2x²+xy-9y²)=x²-3xy+y²+2x²+xy-9y²=3x²-2

1、x-y=a+32x+y=5a二式相加得3x=6a+3,得x=2a+1代入得y=a-2所以方程组解为x=2a+1,y=a-22、2a+1＞a-2,解得a＞-3a-2＞0,解得a＞2综上可得a＞23、

∵x-y=4xy，∴2x+3xy-2yx-2xy-y=2(x-y)+3xyx-y-2xy=8xy+3xy4xy-2xy=112．故答案为：112．

∵A=8x²y-6xy²-3xy,B=7xy²-2xy+5x²y　∴C=3（A+B)　　=3(8x²y-6xy²-3xy+7xy²

已知A=5x^2y-3xy^2+4xy,B=7xy^2-2xy+x^2y.（1）求A-2B的值A-2B=5x^2y-3xy^2+4xy-2*(7xy^2-2xy+x^2y)=5x^2y-3xy^2+4

A=y+2xy记得采纳啊

不会