x2 3x y-3=0求x y的最大值

由y=3xy+x得x-y=-3xy2x+5xy-2y/x-2xy-y=2（x-y）+5xy/x-y-2xy=-6xy+5xy/-3xy-2xy1/5

y-x-2xy=0y-x=2xyx-y=-2xy(3x+xy-3y)/(y-xy-x)=[3(x-y)+xy]/[(y-x)-xy]=(-6xy+xy)/(2xy-xy)=-5xy/xy=-5

-xy（x^2y^5-xy^3-y)=-(xy^2)^3+(xy^2)^2+xy^2=-(-2)^3+4-2=8+4-2=10

xy-12=4x+y≥2√(4xy)=4√(xy)xy-4√(xy)-12≥0(√(xy)-6)(√(xy)+2)≥0√(xy)≤-2,√(xy)≥6因为√(xy)≥0所以√(xy)≥6xy≥36所以

(x+1)平方+y-1的绝对值=0x+1=0y-1=0x=-1y=12（xy-5xy平方）-（3xy平方-xy）=2xy-10xy^2-3xy^2+xy=3xy-13xy^2=-3+13=10

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

平方和绝对值都大于等于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+1=0,y-1=0x=-1,y=1后面漏了平方吧原式=2xy-2xy²-3xy+xy&su

(x+1)^2+|y-1|=0(x+1)^2>=0|y-1|>=0x+1=0,y-1=0x=-1,y=12(xy-5xy的平方)-(3xy的平方-xy)=2xy-10xy^2-3xy^2+xy=3xy

条件是(x+1)^2+|y-1|=0,是吗?如果是它的话,那么x=-1,y=1.带入原式,得值为2

（x+1)^2+|y-1|=0x+1=0x=-1y-1=0y=12（xy-5xy^2)-(3xy^2-xy)=2xy-10xy²-3xy²+xy=3xy-13xy²=3x

y-x-2xy=0所以x-y=-2xyy-x=2xy所以原式=[3(x-y)+xy]\[(y-x)-xy]=[3×(-2xy)+xy]\(2xy-xy)=-5xy\xy=-5

x^2+y^2+2x-4y+1=(x+1)^2+(y-2)^2=4,所以原方程表示圆心为（-1,2),半径为2的圆；（1）y/（x-4）=(y-0)/(x-4),可理解为圆上点（x,y)到（4,0）点

dx/dy-3xy=xy^2dx/x=(y^2+3y)dy两边积分得：lnx=y^3/3+3y^2/2+c==>x=exp(y^3/3+3y^2/2+c)=Cexp(y^3/3+3y^2/2)C常数

(x+y)^2>=0,(y-1)^2>=0,因此y=1,x=-1.原式=2(-1-5)-(-3+1)=-10再问：打错了是已知(x+1)的平方+(y-1)的绝对值=0,求2(xy-5xy的平方）-（3

16524

3(x^2-xy)-xy+y^2=3(x^2-xy)-(xy-y^2)=3*5-(-3)=15+3=18

(x+1)²+|y-1|=0两个非负数的和为0,这两个非负数都为0x+1=0,y-1=0x=-1,y=12(xy-5xy²)-(3xy²-xy)=2xy-10xy

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

∵x-y=4xy∴原式=[2(x-y)+3xy]/[-(x-y)-2xy]=(8xy+3xy)/(-4xy-2xy)=11xy/(-6xy)=-11/6