2x+2x+2y=420,和2y+3y+3x=420怎样计算出x与y是多少?

x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2 (x-y) (x-2y)+(x+2y) (x-3y)-2(x-3y) (x-4y)= (x+y)(x-y)+(x-y)平方-(x-y)(3x-y) 其中x=-2 y=3分之一 已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) 5X+Y=3 X+5Y=2 求x和y.5X+Y=3X+5Y=2求x和y. (x+y)(2x-3y)=? x+y=1 5x-2y=8 3x-y=7 2x-y=3x表示y和用y表示x 【2(x-y)^3-8(x-y)^2(x+y)+6y(x-y)^2】/2(x-y)^2= 已知x-y=3,求[（x+y)(x-y)-(x-y)^2+2y(x-y)]除以的值 已知3x =2y 求x/x+y+y/x-y-y²/x²-y² x(x-y)2-(y-x)3 y+y'-2y=2x 微分方程y - 2y' + y = x 化简y(x+y)+(x+y)(x-y)-x^2 计算：y(x-y)^2+(y-x)^3=? y'=(2x+y)/(3x-y)微分方程通解 12y(x-y)^2-8(x-y)^3=? 计算：x+2y/x-y+2x/y-x-3y/x-y