原式=1? a?1 a ÷ a2?1 a(a+2) =1? a?1 a ? a(a+2) (a+1)(a?1) =1? a+2 a+1 = a+1?(a+2) a+1 = a+1?a?2 a+1 =? 1 a+1 ，原式=- 1 2 ?1+1 =- 1 2 =- 2 2 ．
