A=x²+2xy,B=-xy+y²
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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^2-3xy+4y^2=(x^2+xy)+4(y^2-xy)=a+4
解2A-[B-(B-A)+2A+B]=2A-[B-B+A+2A+B]=2A-(B+3A)=-B-A=-(x²+2xy+y²-3)-(x²-2xy+y)=-x²-
a=x平方-2xy+y平方,b=x平方+2xy+y平方所以x²+y²=a+2xy=b-2xy所以4xy=b-a
解∵2x²+xy=a∴4x方+2xy=2a----------(1)3y²-2xy=b∴9y方-6xy=3b-----------(2)(1)-(2)得:4x方+8xy-9y方=2
(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
解题思路:题不完整,请补充解题过程:.最终答案:略
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
解C=(-A-B)/2=-2x^2y+xy-2xy^2C-A=-7x^2y-3xy+xy^2
A=5x^2y-3xy^2+4xyB=7xy^2-2xy+x^2y2C=-A-B2C-2A=-3A-B=-15x^2y+9xy^2-12xy-7xy^2+2xy-x^2y=-16x^2y+2xy^2-
4x²+8xy+9y²=2x²+2x²+xy+xy+6xy+9y²=2a+9y²+6xy=2a+3y²+2xy+3y²+
C=3A+3B所以C-2A=3A+3B-2A=A+3B=8x²y-6xy²-3xy+21xy²-6xy+15x²y=23x²y+15xy²-
∵A=8x²y-6xy²-3xy,B=7xy²-2xy+5x²y ∴C=3(A+B) =3(8x²y-6xy²-3xy+7xy²
4x的平方+8xy+9y的平方=4x的平方+2xy+9y的平方+6xy=2a+3
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
①:A=5x²y-3xy²+4xy=xy(5x-3y+4)B=7xy²-2xy+x²y=xy(7y-2+x)A-2B=xy(5x-3y+4)-2[xy(7y-2
A=3X^2-2XYB=Y^2+XYC=X^2-XY+Y^2=(x-y)^2-xy题目不完整再问:不用了