如果x y=1则代数式1 2x² xy 1 2y²
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1/2xy(x²-2xy+y²)=1/2xy(x-y)²=10
x的平方-8+1/3xy-3y的平方+3kxy=x的平方-8+(1/3+3k)xy-3y的平方这个代数式中不含xy项则1/3+3k=03k=-1/3k=-1/9
x^2-8+3分之1xy-3y^2+3kxy=x^2-8+(3分之1+3k)xy-3y^2不含xy项则系数为03分之1+3k=0k=-9分之1
绝对值大于等于0,相加等于0,若有一个大于0,则另一个小于0,不成立所以两个都等于0所以x+y+1=0xy+3=0xy=-3x+y=-1两边平方x^2+2xy+y^2=(-1)^2x^2+y^2=1-
利用分数的性质(或者叫商不变原理),将分式的分子和分母同时除以xy就行了.
答:x+y=-1,xy=-2-5(x+y)+(x-y)+x(xy+y)=-5x-5y+x-y+xy(x+1)=-4x-6y+(-2)(x+1)=-4x-6y-2x-2=-6x-6y-2=-6(x+y)
(5x+3xy-5y)/(x-2xy-y)=(5/y+3-5/x)/(1/y-2-1/x)分子分母同时除以xy=[-5(1/x-1/y)+3]/[-(1/x-1/y)-2]=(-15+3)/(-3-2
∵1-8x≥0,8x-1≥0,∴x=18,y=12,∴代数式xy+yx+2-xy+yx−2=14+4+2-14+4−2=52-32=1.故选:B.
x3+3xy+y3=(x+y)(x2-xy+y2)+3xy,=(x2-xy+y2)+3xy,=(x+y)2-3xy+3xy,=1.
(1)A-2B=2x2+3xy+2y-1-2(x2−xy+x−12)=2x2+3xy+2y-1-2x2+2xy-2x+1=5xy+2y-2x,当x=y=-2时,A-2B=5xy+2y-2x=5×(-2
(4xy+12y)+[7x-(3xy+4y-x)]=4xy+12y+7x-3xy-4y+x=xy+8x+8y=xy+8(x+y)=(-2)+8*3=-2+24=22
1/2x^2+xy+1/2y^2=1/2(x^2+2xy+y^2)=1/2(x+y)^2=1/2
由题意可得x-1=0,-y2x=0.故x=1y=2.将结果代入所求代数式可知结果为4/3
因为xy/(x+y)=1/2所以x+y=2xy原式=3(x+y)-5xy/(-x-y+3xy)=3*2xy-5xy/(-2xy+3xy)=xy/xy=1
x分之1-y分之1=-3所以(y-x)/xy=-3y-x=-3xy从而3x-2xy-3y分之x+3xy-y=(3xy+3xy)/(3×3xy-2xy)=6/7
(1)∵A=2x2+3xy+2y-1,B=x2-xy+x-12,x-y=-1,xy=1,∴A-2B=(2x2+3xy+2y-1)-2(x2-xy+x-12)=2x2+3xy+2y-1-2x2+2xy-
x^3+1/2xy-3y^2+2kxy-1=x^3+(1/2+2k)xy-3y^2-1代数式中x^3+2分之1xy-3y^2+2kxy-1中不含xy项,即xy项系数为0,故1/2+2k=0k=-1/4
x^2+y^2=x^2+y^2+2xy-2xy=(x+y)^2-2xy=a^2-2·(1/4a)=a^2-a/2【若你想表示的实际是:xy=1/(4a),则结果为:a^2-1/(2a)】
1/x-1/y=3(y-x)/(xy)=3y-x=3xyx-y=-3xy(2x-14xy-2y)/(x-2xy-y)=[2(x-y)-14xy]/[(x-y)-2xy]=(-6xy-14xy)/(-3