a₁=S₁=1/4（a₁+1）²，解得a₁=1an=Sn-Sn-1=1/4（an+an-1 +2）（an-an-1）4an/（an-an-1）=an+an-1 +22（an+an-1）/（an-an-1）=an+an-1an+an-1=0或an-an-1=2所以{an}的通项公式是（-1）∧（n+1）或an=2n-1
