计算 (xy+xy)÷(x+y) (4a-12ab+9b)÷(3b-2a) (4x-6xy)÷(2-3y) [(x+3y)-4x]÷(x+y) 解方程 81x-4=0 (x-2)=4x-8 已知x-y=3,xy=2,求xy-2xy+xy

1.(xy+xy)÷(x+y) =xy(y+x))÷(x+y) =xy 2.(4a-12ab+9b)÷(3b-2a) =(2a-3b)÷(3b-2a) =-(2a-3b) 3.(4x-6xy)÷(2-3y) =2x(2-3y)÷(2-3y) = 2x 4.[(x+3y)-4x]÷(x+y) =(x+3y+2x)(x+3y-2x)÷(x+y) =3(x+y)(3y-x)÷(x+y) = 3(3y-x) 5.81x-4=0 (9x+2)(9x-2)=0 x1=-2/9,x2=2/9 6.(x-2)=4x-8 (x-2)-4(x-2)=0 (x-2)(x-2-4)=0 x1=2,x2=6 7.xy-2xy+xy =xy(x-2xy+y) =xy(x-y) =2×3 =18