一道简单的数学题怎么做

Sn + Sn+1 = kan+1
Sn-1 + Sn = kan(n>=2)
=>
Sn+1 - Sn-1
= kan+1 - kan
=an+1 + an (n>=2)
=>
an+1 = (k+1)/(k-1)*an(n>=2)
当n=1时
S1 + S2 = 2a1 + a2 = ka2
=>
a2 = 2/(k-1)*a1
要使其为等比数列
=>
2/(k-1) = (k+1)/(k-1)
无解，
所以不可能为等比数列

Sn + Sn+1 = kan+1
Sn-1 + Sn = kan(n>=2)
=>
Sn+1 - Sn-1
= kan+1 - kan
=an+1 + an (n>=2)
=>
an+1 = (k+1)/(k-1)*an(n>=2)
当n=1时
S1 + S2 = 2a1 + a2 = ka2
=>
a2 = 2/(k-1)*a1
要使其为等比数列
=>
2/(k-1) = (k+1)/(k-1)
无解，
所以不可能为等比数列
祝你学习进步