f(x)=log^2(x+1)/(x-1)+log^2(x-1)+log^2(p-x)
定义域：(x+1)/(x-1)＞0,且x-1＞0,且p-x＞0
x＜-1或x＞1,且x＞1,且x＜p
∴1＜x＜p
f(x)=log2 (x+1)/(x-1)+log2 (x-1)+log2 (p-x)
=log2 [(x+1)/(x-1) * (x-1) * (p-x) ]
=log2 [(x+1) (p-x) ]
=log2[-x^2+(p-1)x+p]
令g(x)=-x^2+(p-1)x+p,其最大值：[4*(-1)*p-(p-1)^2]/[4*(-1)]=(p+1)^2/4恒大于0
另外,对称轴x=(p-1)/2应符合定义域1＜x＜p的要求：
1＜(p-1)/2＜p
2＜p＜2p+1
故P＞3