解(1)由题意有当n=1时S1=((a1+1)/2)^2 a1=S1 所以a1=1 (2)an=Sn-S(n-1)=(an+1)^2/4-(a(n-1)+1)^2/4 得(an-a(n-1)-2)(an+a(n-1))=0 显然an>0,所以n>=2时an为等差数列 所以an=2n-1 带入n=1时验证得之 当n属于正整数时an=2n-1
S1=a1=(a1+1/2)^2=a1^2+a1+1/4即a1=a1^2+a1+1/4a1^2+1/4=0无解