Question

一一ㄑ

求解！！

符合
→ = 2n+2
ROA
數列〈ar〉滿足a+2a2+3ag +‥+nam =n²-n-1,則an?
+ +E+SH
(0²2)
答:qq = -1, an =
2

Answer 1

✨ 最佳解答 ✨

qn

n=1: a₁=1²-1-1=-1

a₁+2a₂+3a₃+⋯+naₙ=n²-n-1
a₁+2a₂+3a₃+⋯+naₙ+(n+1)aₙ₊₁=(n+1)²-(n+1)-1=n²+n-1
下式減去上式
(n+1)aₙ₊₁=2n
aₙ₊₁=2n/(n+1)
aₙ=2(n-1)/n