a是底,a>0,a≠1
x>3
loga(x-3)=1+loga(x+2)+loga(x-1)化为ax^2 +(a-1)x+(3-2a)=0 有根
(a-1)^2 -4a(3-2a) ≥0
①-(a-1)/(2a)>3 必有根
②-(a-1)/(2a)