lna/ln(a- 1)>ln(a+ 1)/lna

So lna * lna >: ln (a-1) ln (a+1)

So lna >: [lnln (a-1)+lnln (a+1)]/2 (1).

Since lnlnx is a convex function (when x >; = 1/e) and

Because of a>2, a> 1/e, a-1> 1/e，a+ 1 & gt； 1/e

So it is proved (1).