已知|2x+1|+1/2(3x-2y-5/2)的平方=0 则（xy)的1999次方是多少?

已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) 1 已知1/X+1/Y=1/X+Y 则 Y/X+X/Y=2 已知1/X-1/Y=5,则3X+5XY-3Y/X-3XY-Y= 已知：2x+y=6,x-3y=1 求7y(x-3y)(x-3y)-2(3y-x)(3y-x) 已知x-y=1,求[(x+2y)^2+(2x+y)(x-4y)-3(x+y)(x-y)]除以y的值大神们帮帮忙 已知x-y=1,求[(x+2y)²+(2x+y)(x-4y)-3(x+y)(x-y)]÷y的值 (3x-2y)(4x-5y)-11(x+y)(x-y)+5xy,已知X=3又1/2,y=2又1/3 已知x.y满足(x-y-2≤0,x 2y-5≥0,y-2≤0 则3x+y/x+1得多少 已知x=1/3,y=-1/2,求代数式x-(x+y)+(x+2y)-(x+3y)+(x+4y)-(x+5y)+...-(x+2009y)的值. 已知x=1/3,y=-1/2,求代数式x-(x+y)+(x+2y)-(x+3y)+(x+4y)-(x+5y)+...-(x+2009y)的值. 已知1/x+1/y=5,求(2x-3y+2y)/(x+2xy+y)的值 已知1/x+1/y=5,求2x-3y+2y/-x+2xy-y 已知1/x-1/y=3,则5x+3y-5y/x-2xy-y的值 已知x/1-y/1=3,则5x+xy-5y/x+2y-y的值为 1、(-y^3)^5/y^3/ y^2+2(-y)^102、(x-y)^7/(y-x)^6+(x+y)^3/(x+y)^23、已知X^a=5,x^b=3,求X^(3a-2b)的值 已知x(x+1)-(x²+y)=3求2/x²+y²-xy 已知x=2+根号3,y=2-根号3,计算代数式(x+y/x-y-x-y/x+y)乘以(1/x^2-1/y^2) 已知x-y=-3y+5,则式子x+2y-1的值是? 已知-1《x+y《1,-1《x-y《1.求3x-2y的最小值