试讨论函数f（x）=logax+1/x-1（a＞0且a≠1）在（1，+∞）上的单调性，并予以证明．

设u=x+1x-1，任取x2＞x1＞1，则u2-u1=x2+1x2-1-x1+1x1-1=(x2+1)(x1-1)-(x1+1)(x2-1)(x2-1)(x1-1)=2(x1-x2)(x2-1)(x1-1)．∵x1＞1，x2＞1，∴x1-1＞0，x2-1＞0．又∵x1＜x2，∴x1-x2＜0．∴2(x1-x2)(x2-1)(x1-1)＜0，...