证明：代数式[(x+y)(x-y)-(x+y)^2-2y(x-y)-2xy]/xy 的值为x,y的值无关 解方程 (x+1)^5/(-1-x)^4=3x+7

[(x+y)(x-y)-(x+y)^2-2y(x-y)-2xy]/xy ={(x+y)[(x-y)-(x+y)]-2y(x-y)-2xy}/xy ={(x+y)[(x-y-x-y)]-2y(x-y)-2xy}/xy ={-2y(x+y)-2y(x-y)-2xy}/xy ={-2y[(x+y)+(x-y)]-2xy}/xy ={-2y[x+y+x-y]-2xy}/xy ={-4xy-2xy}/xy ...