{5x-8y=4 -3x y=-0.5,解二元一次方程

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（5X-4Y-3XY）-（8X-Y+2XY）=-(3X+3Y)-5XY=-3*6+4*5=2

Solution:x^2-2xy+3y^2=9(1)4x^2-5xy+6y^2=30(2)Eq(1)*5-Eq(2)*2,wehavex^2-y^2=5(3)Eq(2)-Eq(1),wegetx^2+

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

楼主是不是把题写错了呀,应该是（X+2)^2+/Y+1/=0吧因为（X+2)^2大于等于0/Y+1/大于等于0所以只有同时为0时,和才为0即X=-2Y=-1带入原式=4

（x+2）平方+|y+1|=0则x+2=0,y+1=0所以x=-2.y=-1xy平方=-2.x平方y=-45xy*-｛2x*y-【3xy*-（4xy*-2x*y）】｝=5*（-2）-【2*（-4）-3

根据已知得到x=-2y=-1原式=5xy^2-{2x^2y-[3xy^2-(4xy^2-2x^2y)]}=5xy^2-{2x^2y-[3xy^2-4xy^2+2x^2y]}=5xy^2-{2x^2y-

解2(x+3y-2xy)-(4x+8y-2xy)=2x+6y-4xy-4x-8y+8xy=-2x-2y+4xy=-2(x+y)+4xy=-2×5+4×3=12-10=24x²-3y²

(3xy+2)^2+|7-x-y|=0,则3xy+2=0,7-x-y=0,即x+y=7,xy=-2/3(5xy+10y)-[-5x-(4xy-2y+3x)]=5xy+10y-(-5x-4xy+2y-3

（x+2）^2+|x+y+5|=0,x+2=0,x+y+5=0x=-2,y=-33(x^2)y-2(x^2)y+2xy-(x^2)y+4x^2-xy=4x^2+xy=4*(-2)^2+(-2)*(-3

把第一个式子分开来看,x的平方-8x+16+y的平方+6Y+9=0,然后就有两个完全平方了,（x-4）的平方+（y+3）的平方=0然后可以得出x=4,y=-3,然后带进去就可以得出答案

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

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

（3x-2y+8xy）-（x-4y-5xy）=3x-2y+8xy-x+4y+5xy=2x+2y+13xy=2(x+y)+13xy=2×3+13×(-2)=-20

2x＋y＋3=xy,①若x=1,则y不存在,此时5x＋4y无最值；②若x≠1,则y=(2x＋3)/(x－1),M=5x＋4y=5x＋(8x＋12)/(x－1)=(5x²＋3x＋12)/(x－

x+y=5xy（2x-3xy+2y)/(x+2xy+y）=[2（x+y）-3xy]/[(x+y)+2xy]=(2×5xy-3xy)/(5xy+2xy)=7xy/7xy=1再问：若x＋1/x＝3,求(x

因为,x-y=3xy所以：-3x+6xy+3y/[(7x-5y)-9xy-(3x-y)]=[-3(x-y)+6xy]/[(7x-5y)-9xy-(3x-y)]=[-3*3xy+6xy]/[7x-5y-

x+2=0,x+y+5=0x=-2,y=-33x^2y+{-2X^2y-[-2xy+(x^2y-4x^2)]-xy}=3x^2y-2X^2y+2xy-x^2y+4x^2-xy=4x^2+xy=4*4+

[-(x-y)^2/xy]^-4*(y^2-xy/x)^3*(x^4/y^10)÷(xy-y^2/x)^-5=-y(y-x)^29^-x*27^y=3^-2x*3^3y=3^(-2x+3y)=3^(-

2x^2-3xy-2y^2=0（x-2y)(2x+y)=0x-2y=0或2x+y=0x=2y或y=-2x当x=2y时(4x^2-5xy+y^2)/(3x^2+3xy+y^2)=（4×4y²-