3x y=2k 2y-x=3 满足x1 则k的取值范围为

x^2+(4-3y)x+3y^2-18y+52=0x=0.5(3y-4+sqrt((4-3y)^2-4(3y^2-18y+52)))=0.5(3y-4+sqrt(-3(y-8)^2))或x=0.5(3

答：x>0,y>0x-√(xy)-2y=0(√x-2√y)(√x+√y)=0因为：x>0,y>0所以：√x+√y>0所以：√x-2√y=0所以：√x=2√y所以：x=4y所以：[x+3√(xy)+2y

xy=6/(x+y)xy(x+y)=6,已知x和y是整数,则xy和(x+y)也是整数,而6=2*3=1*6当xy=3时,x+y=2,无整数解当xy=1时,x+y=6,无整数解当xy=6时,x+y=1,

x=6-3y               &nbs

解由题知求xy的最大值,则x,y必定同号,不妨设x,y同正则由x^2+y^2+xy=1/3得1/3=xy+x²+y²即1/3-xy=x²+y²≥2xy即1/3≥

x²+3x+y-3=0x²+2x+x+y-3=0（x+1)²+x+y-4=0x+y=4-(x+1)²因为要使x+y最大,所以（x+1)²一定要取最小值

x,y取值范围如上图,凸点为：(0,1)   (1,0)   (2.5, 2.25)目标函数在凸点的取值：4,1,26.5∴z的取

由x=|y|得x为非负数又|xy|+xy=0所以xy为非正数y为非正数所以原式=（-y）+2x-[-（3y-2x）]（最后一步3y是非正数,2x是非负数,2x一定大于或等于3y,故加负号）=-y+2x

x=-1y=2代入求值就可以

解方程组2x+y＝2k2y−x＝3得：x＝4k−35y＝2k+65因为x＜1，y＞1，所以4k−35＜12k+65＞1，解得-12＜k＜2，所以k为0或1．即，整数k的个数有2个．

若|x+2|+(y-1/2)平方=0,则有：x+2=0且y-1/2=0解得：x=-2,y=1/2所以：3(2x^2y-xy^2)-(5x^2y-4xy^2)这里是不是少打了个y哈!=6x平方y-3xy

x-2y=3m-2x+y=10y=4-mx=m+6xy4或m

分解因式有(x-3y)(2x-y)=0所以有x=3y或2x=y所以x:y=3:1或x:y=1:2

因为2(x-1/2)²+|y-1|=0所以x-1/2=0且y-1=0x=1/2,y=1所以3B-2A=3(2x²-3xy-2y²)-2(3x²-xy+y

x^2+2xy-3y^2=0x^2+2xy+y^2-4y^2=0(x+y)^2=4y^2x+y=2y或x+y=-2yx=y或x=-3y因为两个正实数所以x=yx^2+xy+y^2/x^2-xy+y^2

2x-3>=03-2x>=0∴x=3/2把x=3/2代入y=根号2x-3+根号3-2x+6得y=6∴xy=9xy的平方根是±3

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

1/x-1/y=5即,(y-x)/xy=5即,x-y=-5xy(3x-2xy-3y)/(x+xy-y)=[3(x-y)-2xy]/[(x-y)+xy]=(-15xy-2xy)/(-5xy+xy)=(-

4x-3y=k①2x+3y=5②①-②×2得:4x-3y-4x-6y=k-10-9y=k-10y=-(k-10)/9①+②得:4x-3y+2x+3y=k+56x=k+5x=(k+5)/6因为x

丨x+2丨+（y-1）^2=0丨x+2丨=0,（y-1）^2=0x+2=0,y-1=0x=-2,y=1所以(xy-3x^2)-2(xy-2x^2-1)=(xy-3x^2)-2xy+4x^2+2=-xy