若lg(Xy)lg(X 2y)=lg^2 lgx lgy
解: 2 lg(x-2y)=lgx+lgy==lg(x-2y)^2=lgxy ==(x-2y)^2=xy ==x^2-5xy+4y^2=0 ==(x-4y)(x-y)=0 ==x=4y,or x-y=0 ==x/y=4 or x/y=1 lg2(x/y)=2 or 0
0
解: 2 lg(x-2y)=lgx+lgy==lg(x-2y)^2=lgxy ==(x-2y)^2=xy ==x^2-5xy+4y^2=0 ==(x-4y)(x-y)=0 ==x=4y,or x-y=0 ==x/y=4 or x/y=1 lg2(x/y)=2 or 0