已知1/2|x-2y|+|y-1/2|=0,求7x-3y的值

已知x+y=a,2x-y=-2a,求[（x/y-y/x)/(x+y)-x(1/x-1/y)]/[(x+1)/y]的值 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:【(x²+y²)-(x-y)²+2y(x-y)】/4y=1,求4x/4x²-y²-1/2x+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)]÷y的值 已知x,y满足约束条件：x-y+1>=0,x+y-2>=0,x 已知((x+y)平方-(x-y)的平方-2y(x+2分之1y))除以4y=1 已知(2x+1)*2+y*2+2y+1=0 求{(x*2+y*2)-(x-y)*2+2y(x-y)}/(2y) 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=1/2,求2x/(x²-2xy+y² )* (x²-y²/x+y)+2y/x-y 已知x/y=1/2,求2x/(x²-2xy+y² )* (x²-y²/x+y)+2y/x-y 已知集合A={y|y=(1/2)^x,x0}C.{y|y=2} 已知 x-2y=-2 求(2y-x)平方-2x+4y-1 已知(x+y)^2-2x+2y+1=0,则(x+y)^999= 已知集合A={(x,y)|2x-y+2>=0,x-2y+1 已知x平方+y平方+2xy+1=2x+2y,求x+y 已知x平方+y平方-2xy-2x-2y=-1,求x+y x>0 y>0已知x+2y=1求 1/x+y/1最小值