y=(x-1÷2)（x-2) y=3(2x+1)(2-x） 需要用公式法解一遍

已知x-y=1,求[(x+2y)²+(2x+y)(x-4y)-3(x+y)(x-y)]÷y的值 x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2 (x+y)(x-y)+(x-y)^2-(6x^2×y÷2y-2xy^2÷2y)其中x=-3,y=1/3 若2/x-1/y=3,求[y/x-y/x-y(x-y/x-x+y)]/x-2y/x的值 先化简再求值:(x+y)(x-y)+(x^2-2xy+y^2)-(x^2y)^3÷(x^2y)^2,其中x=1,y=2. (3x-y)^2+(3x+y)(3x-y),x=1,y=-2 二元一次方程 ：2(x+y)-(x-y)=3 (x+y)-2(x-y)=1 2(x+y)-3(x-y)=1 6(x+y)+(x-y)=51 {3(x+y)-4(x-y)=4 {x+y/2 + x-y/6=1 变量x,y满足约束条件,x+y>=3,x-y>=-1,2x-y (x-y)^2+(x+y)(x-y) 其中 X =3 Y=-1 (x-y)/(x+y)=3求( 3x-2y-1)/(x+y-5) 先化简,再求值:y(x-y)-x(x+y)/x²-y²÷x²+y²/x+y,其中x=2,y=-1 1-[(x-y)/(x+2y)]÷[(x+y)(x-y)/(x+2y)²] 1-[(x-y)/(x+2y)]÷[(x+y)(x-y)/(x+2y)²]= {(x+y)/2+(x-y)/3=1,(x+y)-5(x-y)=2.求x=?,y=? x+y+2(-x-y+1)=3(1-y-x)-4-(y+x-1),x+y=? (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