2x-5y= -21 4x+3y=23求这方程组?没学会.

已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) (x-y)/(x+y)=3求( 3x-2y-1)/(x+y-5) 已知:3x-5y=0,求x/y,x-y/y,x-y/x {(x+y)/2+(x-y)/3=1,(x+y)-5(x-y)=2.求x=?,y=? 已知2y-x=-3,求[4y(2x-y)-2x(2x-y)]/(2x-y 4x-3y=5 x^2+y^2=1 求x,y 求5x-2y=x-y=4x-3y-2的解 3x+4y-5=0 x^2+y^2=1求x.y 5x+y=2,x-3y=4,求x和y, 5x+y=2 x-3y=4 求x和y 方程式计算5X-2=Y 4X+3=Y 求X.Y 若2x-3y=0,求5x+4y/3x-2y 已知x,y>0 2x+y+3=xy 求5x+4y最小值 若(x*x+y*y)(x*x+y*y)-4x*x*y*y=0,求代数式(x*x+5xy+y*y)/(x*x+2xy+y*y)的值 1.已知:x-2y=3,求[(3x+2y)(3x-2y)-(x+2y)(5x-2y)]除4x 的值 已知x-2y=2011,求[(3x+2y)(3x-2y)-(x+2y)(5x-2y)]÷4x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x-y=1,求[(x+2y)²+(2x+y)(x-4y)-3(x+y)(x-y)]÷y的值