∵an+12+an2+1=2(an+1an+an+1-an)
∴an+12-2an+1?an+an2-2(an+1-an)+1=0
∴(an+1-an)2-2(an+1-an)+1=0
∴(an+1-an-1)2=0
∴an+1-an=1∴{an}为等差数列
∴an=a1+(n-1)?1=n
∴Sn=
+1
a1a2
+…+1
a2a3
1
anan+1
=
+1 1?2
+…+1 2?3
1 n(n+1)
=1-
+1 2
-1 2
+…+1 3
-1 n
=1-1 n+1
=1 n+1
n n+1