4y/3x·x/2y^3= ab^2/2c^2÷-3a^2b^2/4cd(x^2-4y^2)/(x^2-2xy+y^2)除以x-2y/x²-xy 求求啊、、

(x-y) (x-2y)+(x+2y) (x-3y)-2(x-3y) (x-4y)= 2（x+y)-3(x-y)=3 ,4(x+y)+3(x-y)=15 3(x+y)+2(x-y)=36 4(x+y)-5(x-y)=2 （x+y）/2- x-y/2=6 3(x+y)=4(x-y) x+y/3+x-y/2=6 4(x+y)-2(x-y)=40 x+y/2+x-y/3=6,4(x+y)-3(x-y)=-20 {(x+y)/2+(x-y)/3=6 4(x+y)-3(x-y)=-20 4(x+y)-3(x-y)=-20,2/x+y+3/x-y=6 3(x+y)-2(x-y)=11 4(x+y)+3(x-y)=9 {3(x+y)-4(x-y)=4 {x+y/2 + x-y/6=1 4(x-y)-3(x-y)=9 5(x-y)+2(x-y)=11 3(x+y)-4(x-y)=11,2(x-y)+5(x+y)=27 先化简再求值(x-y)(x-2y)+(x-2y)(x-3y)-2(x-3y)(x-4y) x=4 y=5 （2)(x-2)(x+2)-(x+1)(x-3)(3) (ab+1)²-(ab-1)²(4)（2x-y)²－4(x-y)(x+2y) 1.(x-2)(x+2)-(x+1)(x-3)2.(ab+1)^2-(ab-1)^23.(2x-y)^2-4(x-y)(x+2y) 已知2y-x=-3,求[4y(2x-y)-2x(2x-y)]/(2x-y (1)2（a^2-ab)-2a^2+3ab (2)5(2x-7y)-3(4x-10y) (3)(x+y)-[3x+(-x+y)] x+y+2(-x-y+1)=3(1-y-x)-4-(y+x-1),x+y=?