参考下面这个若lg(x-y)+lg(x+2y)=lg2+lgx+lgy,求x/y的值 lg(x - y) + lg(x + 2y) = lg[(x - y)(x + 2y)] lg^2 + lgx + lgy = lg(2xy) 所以： (x - y)(x + 2y) = 2xy x^2 + 2xy - xy - 2y^2 = 2xy x^2 - 2y^2 = xy x/y - 2y/x =

1 设 a = x/y 则有 a^2 - a -