先化简再求值,其中 实数xy满足Y=根号下x-2

xy^3÷(-xy)+(x+2y)(x-2y)=-y^2+x^2-4y^2=x^2-5y^2=2-5=-3再问：不好意思啊！题目......再答：题目怎么了，不影响结果啊。平方还是正的

解3x平方y-[2xy-2(xy-3/2x平方y)+xy]=3x平方y-(2xy-2xy+3x平方y+xy)=3x平方y-(xy+3x平方y)=3x平方y-3x平方y-xy=-xy=-3×(-1/3)

化简为3xy²(xy+2y²)求得24再问：过程呢

原式=2xy^2-4y+xy-xy-3xy^2+4y=-xy^2=-4×（1/2）^2=-1

设xy=(x^3/y)^m*(x^2/y^2)^n=x^(3m+2n)y^(-m-2n)3m+2n=1-m-2n=1m=1,n=-1即有xy=x^3/y*y^2/x^22

原式=[(3-2xy^2)^2+3(2xy^2-3)]/(-xy)=(2xy^2-3)*[(2xy^2-3)+3]/(-xy)（分子提取公因式2xy^2-3）=(2xy^2-3)*(2xy^2)/(-

[2x（x^2y-xy^2）+xy(xy-x^2)]÷x^2y=(2x^3y-2x^2y^2+x^2y^2-x^3y)÷x^2y=(x^3y-x^2y^2)÷x^2y=x-y=2008-2004=4

[2x（x^2y-xy^2）+xy(xy-x^2)]÷（x^2y）=[2x²y(x-y)+x²y(y-x)]÷(x²y)=2(x-y)+(y-x)=x-y已知x=2008

答案:5.(用线性规划的知识解决)由y≥1,y≤2x-1作出可行域(∵直线x+y=m不确定,∴可行域暂时不确定,但不影响解题)∵目标函数z=x-y的最小值为-1∴y=x-z截距最大时,z最小,为-1,

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

z=3x+y=13(x+2y)/6+5(x-4y)/6当x=5,y=2时取到,z最大值17

x^2y-2（2xy^2-3x^2y-3）3xy^2,其中x,y满足|x-2|（y1=x²y-4xy²+6x²y+6-3xy²=7x²y-7xy

(-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

(2x-3y+5xy)-(x-4y-3xy)=2x-3y+5xy-x+4y+3xy=2x-x-3y+4y+5xy+3xy=x+y+8xy=(x+y)+8(xy)=-3+8*(-4)=-3-32=-35

解题思路：求值解题过程：varSWOC={};SWOC.tip=false;try{SWOCX2.OpenFile("http://dayi.prcedu.com/include/readq.php?

y=√(x-3)+√(6-2x)+2被开方数要大于等于0x-3≥0且6-2x≥0x≥3且x≤3所以x=3y=0+0+2=2原式=√(2x)×√(x/y)×[√(y/x)/√(1/y)]=√(2x×x/

原式=1/9x²y²(2x²y-xy²-2x²y+2xy²)=1/9x²y²*xy²=1/9x³y&

根号2x乘以根号y分之x乘以（根号x分之y除以根号y分之一）=根号2x^2/y*（根号y/x*根号y）=根号2x^2/y*根号y^2/x=根号2x/y再代入x、y的值就可以了.

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

原式=2x2-2xy-6x2+9xy-2x2+2x2-xy+y2=-2x2+5xy+2y2，当x=-1，y=-2时，原式=-2+10+8=16．