a>0a-1<0则（a^2-2a+1）/(a-1)-√(a^2-2a+1)/(a^2-a)-1/a=(a-1)^2/(a-1)-√(a+1)^2/a(a-1)-1/a=a-1-(1-a)/a/(a-1)-1/a=a-1+1/a-1/a=a-1=1-√3
