(a*a/a-1)-a-1
=a*a/a-1-(a+1)
=(a*a)/(a-1)-( a+1)*(a-1)/(a-1)
=(a*a)/(a-1)-(a*a+1)/(a-1)
=(a*a-a*a+1)/(a-1)
=1/(a-1)
思考很累,打字很累,求采纳!