lg(x+2y)+lg(x-y)=lg2+lgx+lgy
lg(x+2y)(x-y)=lg2xy
(x+2y)(x-y)=2xy
x^2+xy-2y^2=2xy
x^2-xy-2y^2=0
(x-2y)(x+y)=0
x=2y,x=-y
由定义域,x>0,y>0
所以x=-y不成立
所以x=2y
x/y=2