9x²-y²-4y²-4

(2x-y)²-4(x-y)(x+2y) 化简：（2x-y)²-4(x-y)(x+y) (x+y)²+4(x+y)-5 计算：(x+y)²-4(x+y)(x-y)+4(x-y)² 化简 3(X-Y)²-4(X-Y)+7(X-Y)-6(X-Y)² 计算 [12(x+y)³(y-x)]³÷[4(x+y)²（x-y)]² （x-2y）²+（2x-4y)(x+y)+(x+y)² 因式分解：(x-y)(3x-7y)²-4(x-y)(x+y)² 因式分解：25(x+y)²-9(x-y)²；（x+y）²-4（x+y-1）. 因式分解 （1）.(x+y)(x+y-6)+9 （2）.x²-16y²-x-4y 函数f(x,y)=x²+y²-2x+4y+9的最小值 已知x/y=2,求2x(x+y)-y(x+y)/4x²-4xy+y²