min1986
幼苗
共回答了18个问题采纳率:88.9% 举报
因为
S(n) = n^2 + 10n
S(n+1) = (n+1)^2 + 10(n+1)
= n^2 + 2n + 1 + 10n + 10
= n^2 + 12n + 11
a(n+1) = S(n+1) - S(n)
= n^2 + 12n + 11 - n^2 - 10n
= 2n + 11
= 2(n + 1) + 9
所以
a(n) = 2n + 9
又因为
b(n) = |a(n)|
所以
b(n) = |2n + 9| = 2n + 9
1年前
6