1.
2Sn=An²+An
2Sn+1=A(n+1)²+A(n+1)
相减得:
(An+1 + An)(An+1 - An - 1)=0
An+1 + An=0或An+1 - An - 1=0
数列{An}的各项均为正数
则An+1 - An - 1=0
An为公差为1的等差数列
2Sn=An²+An
2a1=a1²+a1
a1=0(舍)或a1=1
An=a1+(n-1)=n
2.
(1)A4=A1+3d=25+3d=16,d=-3
An=25-3*(n-1)=28-3n
(2)An
1.
2Sn=An²+An
2Sn+1=A(n+1)²+A(n+1)
相减得:
(An+1 + An)(An+1 - An - 1)=0
An+1 + An=0或An+1 - An - 1=0
数列{An}的各项均为正数
则An+1 - An - 1=0
An为公差为1的等差数列
2Sn=An²+An
2a1=a1²+a1
a1=0(舍)或a1=1
An=a1+(n-1)=n
2.
(1)A4=A1+3d=25+3d=16,d=-3
An=25-3*(n-1)=28-3n
(2)An