当a为何值时,关于x的方程2lgx-lg(x-1)=lga无解?

2lgx-lg(x-1)=lga
lgx^2-lg(x-1)=lga
lgx^2/(x-1)=lga
x^2/x-1=a
f(x)=x^2/(x-1)
=[(x-1)^2+2(X-1)+1]/(x-1)
=(x-1)+1/(x-1)+2
由题目 可知:
x-1>0
f(x)>=4
所以
当a4,有两个解