a^2+a/a^2-1+（a^2-a分之根号下a^2-2a+1）
=[a(a+1)]/[(a+1)(a-1)]+[根号下(a-1)^2]/[a(a-1)]
=a/(a-1)+|a-1|/[a(a-1)]
当a-1>=0,即a>=1时,|a-1|=a-1
原式=a/(a-1)+1/a
当a-1