当x y=8,x-y=2时,求代数式x^2-xy y^2的值.

1/X-1/Y=3分子分母同除以xy=(1/y-2-1/x)/(2/y+3-2/x)=(1*3-2)/(2*3+3)=1/9

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

=(x³＋y³)＋xy(x＋y)=(x＋y)(x²－xy＋y²)＋xy(x＋y)=(x＋y)(x²＋y²)=(x＋y)[(x＋y)²

[2x(x²y-xy²)+xy(2xy-x²)]=2x³y-2x²y²+2x²y²-x³y=x³y因

x/y=3=>x=3y原式=(9y²+2*3y*y-3y²)/(9y²-3y*y+y²)=12/7再问：能不能先化简，后代入？再答：可以是可以，x²+

|y-x|-2|xy|=|-3-(-2)|-2|-2×(-3)|=|-1|-2|6|=1-2×6=1-12=11很高兴为您解答,【学习宝典】团队为您答题.请点击下面的【选为满意回答】按钮,

2x²+xy=a3y²+2xy=b4x²+8xy+9y²=2(2x²+xy)+3(3y²+2xy)=2a+3

3xy-[2xy-2(xy-2分之3xy)+xy]+3xy=6xy-[2xy-2xy+3xy+xy)=6xy-4xy=2xy=2×3×3分之1=2

x^4-xy^3-x^3y-3x^2y+3xy^2+y^4=（x^4-x^3y）-xy^3+y^4-3x^2y+3xy^2=x^3(x-y)-y^3(x-y)-3xy(x-y)=x^3-y^3-3xy

=3x^2y-2xy^2+2(xy-3/2x^2y)-xy+3xy^2=3x^2y+xy^2+2xy-3x^2y-xy=xy+xy^2=3*(-1/3)+3*1/9=-2/3

当x=-4y=-2时求代数式-3x平方y+3xy平方+x?+3x平方y-3xy平方-y,=-3x²y+3xy²+x-y+3xy(x-y)=-3xy(x-y)+(x-y)+3xy(x

原式=xy分之(x²-y²)+x(x-y)分之y(x-y)=xy分之(x²-y²)+x分之y=xy分之(x²-y²+y²)=xy分

(1)X+Y=8(2)X-Y=2两式相加：2x=10x=5,将x=5带入（1）中,5+y=8y=3因此,x^2-xy+y^2=5^2-5*3+3^2=25-15+9=192a^2-4b+5=2（a^2

原式=(x+y)/(√x-√y)-(2xy)/(x√y-y√x)=(x+y)/(√x-√y)-(2xy)/[√(xy)(√x-√y)]=(x+y)/(√x-√y)-2√(xy)/(√x-√y)]=[(

(x^4-y^4)/(x^2-2xy+y^2)÷(x^2+y^2)/(y-x)=(x^2-y^2)(x^2+y^2)/(x^2-2xy+y^2)*(y-x)/(x^2+y^2)=(x^2-y^2)/(

（1）当1\x-1\y=3时求2x+3xy-2y\x-2xy-y的值=(2/y+3-2/x)/(1/y-2-1/x)=(2×(-3)+3)/(-3-2)=-3/(-5)=3/5;（2）求代数式x四次方

1/x-1/y=2时(y-x)/xy=2y-x=2xy2x+3xy-2y/x-2xy-y=[3xy-2(y-x)]/[-2xy-(y-x)]=-xy/-4xy=1/4

原式分子分母同除以y²原式=[(xy+y²)/y²]/[(x²-xy)/y²]=[(x/y)+1]/[(x/y)²-(x/y)]=(3/4+

分式(xy+y^2)/(x^2-xy)=(x/y+1)/[(x/y)^2-x/y](分子分母同时除以y^2)=(3/4+1)/(9/16-3/4)(代值)=(7/4)/(-3/16)=-28/3

原式=(x-y)/x/((x^2-2xy+y^2)/x)=(x-y)/x乘以(x/(x^2-2xy+y^2))=(x-y)/x乘以(x/(x-y)^2)=1/(x-y)当x=2008,y=2009原式