已知xy =1,求代数式-3-搜答案-搜狗做题网

xy^2*(-x^2y^2)*（1/2xy^3)^2=xy^2*(-x^2y^2)*（1/4x²y^6)=xy^2*(x^4y^8)*(-1/4)=(-1/4)*xy²*(xy&#

-x的平方y-xy平方=-XY(Y+X),再把x+y=3,xy=2代入结果为=-XY(Y+X）=-2乘3=-6

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-

（xy+5x-2y）-（-3xy+2x-5y）=xy+5x-2y+3xy-2x+5y=4xy+3x+3y=4xy+3（x+y），当x+y=1，xy=-2时，原式=4×（-2）+3×1=-8+3=-5．

xy/x+y=3xy=3(x+y)3x-5xy+3y/-x+3xy-y=(3x+3y)-5*3(x+y)/[-x-y+3*3(x+y)]=-12(x+y)/8(x+y)=-3/2望采纳,谢谢!

解x+2y=2xy=12x+4y+3xy+1=2(x+2y)+3×1+1=2×2+3+1=4+4=8

-5再问：过程再答：

5xy+4x+7y+6x-3xy-4xy+3y=5xy-3xy-4xy+4x+6x+7y+3y=（5-3-4）xy+（4+6）x+（7+3）y=-2xy+10x+10y=-2xy+10（x+y）因为x

∵(x+1)²+|y+2|=0∴要使等式成立,则x+1=0且y+2=0即x=-1,y=-2∴5xy-3/2x³y²-4xy+1/2y²x³-1/2xy

2(x+y)=-6x+y=-3(x+2)-(3xy-y)=x+2-3xy+y=x+y+2-3xy=-3+2-3=-4

代数式可化为2x+2xy-xy+3y+x+xy=3x+3y+2xy=3（x+y）+2xy=3×（-2）+6=0a^2-b^2=15 a^2-2ab+b^2=5&nbs

x=-1y=2代入求值就可以

原式=-2x^2-2y^2-3xy-11xy=-2*7-14*(-1)=0

x2+2xy-3y2=x2-xy+3xy-3y2=x2-xy+3（xy-y2），∵x2-xy=3，xy-y2=-5，∴x2+2xy-3y2=3+3×（-5）=-12．

5x^2-(3xy+4y^2)-(11xy-2y^2)-7x^2=5x^2-3xy-4y^2-11xy+2y^2-7x^2=-2x^2-2y^2-14xy=-2(x^2+y^2)-14*xy=-2*7

(5x+xy-5y)/(x-xy-y)=(5/y+1-5/x)/(1/y-1-1/x)=(1-3)/(-1-3)=1/2

∵|x+y+1|≥0,|xy-3|≥0|x+y+1|+|xy-3|=0,∴x+y+1=0,即x+y=-1xy=3xy3+x3y=xy(x²+y²)=yx[(x+y)²-2

（1）x²+4xy+3y²=x²+xy+3y²+3xy=(x²+xy)+3(y²+xy)=3-6=-3（2）x²-y²=

xy/x+y=3xy=3（x+y）3x-5xy+3y/-x+3xy-y=3x-15（x+y）+3y/-x+9（x+y）-y=-12(x+y)/8（x+y）=-3/2

2x²-xy-3y²=2x²+2xy-3xy-3y²=2(x²+xy)-3(xy+y²)已知x²+xy=3,xy+y²=