x^2 2y^2-3xy=1 ,求x^2 y^2的最值

分子分母同时除以xy则分子得2（1/x+1/y）-3=2*5-3=7分母得3（1/x+1/y）+2=3*5+2=17则得7/17

=-x-(2y-2+3x)+2(x+4)=-x-2y+2-3x+2x+8=-4x-2y+10

/>1/x-1/y=3y-x/xy=3y-x=3xyx-y=-3xy所以(2x+3xy-2y)/(x-y-2xy)=[2(x-y)+3xy]/(x-y-2xy)=[2(-3xy)+3xy]/(-3xy

因为:1/x-1/y=3(y-x)/xy=3x-y=-3xy（1）又因为：(2x+3xy-2y)/(x-2xy-y)=[2（x-y）+3xy]/[(x-y)-2xy]代入（1）得：（-6xy+3xy）

1上下同除以xy,原式=(2/y-2/x-3)/(1/y-1/x-2)=6/52原式两边平方可得x平方+x平方分之一=11(2)所求式子平方,即原式的平方=x平方+x平方分之一+2=13,所以原式=正

(-2xy+2x+3y)-(3xy+2y-2x)-(x+4y+xy)=-6xy+3x-3y=-6×(-2)+3×1=15

1/x-1/y=3(y-x)/xy=3y-x=3xyx-y=-3xy(2X+3XY-2Y)/(X-2XY-Y)=[2(x-y)+3xy]/[(x-y)-2xy]=(-6xy+3xy)/(-3xy-2x

原式=3x-3y-6xy=3-12=-9

y-x=3xy（3y+xy-3x）/（2x-xy-2y）=10xy/(-7xy)=10/7

1/x-1/y=1/3(2x+3xy-2y)/(x-3xy-y)分子分母同除以xy：={2/y+3-2/x}/{1/y-3-1/x}={-2(1/x-1/y)+3}/{-(1/x-1/y)-3}={-

1/x-1/y=(y-x)/xy=3y-x=3xy所以x-y=-3xy原式=[3(x-y)-5xy]/[2(x-y)+3xy]=[3(-3xy)-5xy]/[2(-3xy)+3xy]=-14xy/(-

3/(x-y)=1/xyx-y=3xyy-z=-3xy原式=[(y-x)-2xy]/[2(x-y)+3xy]=[(-3xy)-2xy]/[2(3xy)+3xy]=-5xy/9xy=-5/9

(-2xy+2x+3y)-(3xy+2y-2x)-(x+4y+xy)=-2xy+2x+3y-3xy-2y+2x-x-4y-xy=-6xy+3x-3y=-6xy+3*(x-y)当时,原式=-6*1+3*

x^3y-2x^2y^2+xy^3=xy(3x^2-4xy+y^2)=xy(3x-y)(x-y)x-y=-1,xy=3y(y-1)=3

分数可以打清楚点吗?不然不知道到底哪几项在分子上再问：/前面都是分子再答：图片传不上来，我在贴吧发给你行不行？再问：行~~

因为x-y=-2xy所以将x-y都换成-2xy了

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

求多项式2x²-3xy+y²-2xy-2x²+5xy-2y+1的值,其中x=22/7,y=-12x²-3xy+y²-2xy-2x²+5xy-

x(x²+xy+y²)-y(x²+xy+y²)+3xy(y-x)=X^3+X^2Y+XY^2-X^2Y-XY^2-Y^3+3XY^2-3X^2Y=X^3-3X^

(-2xy+2x+3y)-(3xy+2y-2x)-(x+4y+xy)=-2xy+2x+3y-3xy-2y+2x-x-4y-xy=-6xy+3x-3y=-6*(-2)+3*1=15不懂可追问,有帮助请采