>
数学
>
已知数列an满足a1+2a2+3a3+……+nan=n(n+1)(n+2),则它的前n项和Sn=?
(9n+3n²)/2)
人气:446 ℃ 时间:2019-11-07 12:33:19
解答
设a1+2a2+3a3+……+nan=Tn
则Tn=n(n+1)(n+2)
T(n-1)=n(n-1)(n+1)
nan=Tn-T(n-1)=3n(n+1)
an=3(n+1)
Sn=3(1+1)+3(2+1)+...+3(n+1)
=3n(n+3)/2=(3n^2+9n)/2
推荐
设数列{an}的前n项和为Sn,已知a1+2a2+3a3+…+nan=(n-1)Sn+2n (n∈N*). (1)求a2,a3的值; (2)求证:数列{Sn+2}是等比数列.
已知数列an满足a1+2a2+3a3+...+nan=n(n+1)*(n+2),则数列an的前n项和Sn=?
设数列{an}的前n项和为Sn,已知a1+2a2+3a3+…+nan=(n-1)Sn+2n (n∈N*). (1)求a2,a3的值; (2)求证:数列{Sn+2}是等比数列.
已知数列{an}的前n项和为Sn,且 a1+2a2+3a3+…+nan=(n-1)Sn+2n(n∈N*). (1)求数列{an}的通项公式; (2)若p,q,r是三个互不相等的正整数,且p,q,r成等差数列,试判断ap-1,aq-1,ar-
已知数列{an}满足a1+2a2+3a3+…+nan=n(n+1)(n+2),则它的前n项和Sn=_.
过去式 they were sang 还是they was sang 和 ...he were slept 还是 he was slept?.谢
“This is ______ most useful reference book,” a teacher from ______ European country told us in cl
he makes toys in the factory哪里错了
猜你喜欢
解方程:540×1/6=121/2+x,
明矾净水,结晶水合物失水为什么是化学变化?蒸发为什么是物理变化?
如图所示,在Rt△ABC中,AB=AC,∠A=90°,点D为BC上任一点,DF⊥AB于F,DE⊥AC于E,M为BC的中点,试判断△MEF是什么形状的三角形,并证明你的结论.
小学四年下册改学古诗的作文怎么写?
边长为2的正三角形的斜二测直观图的面积为 _ .
一个长8分米宽5分米高3分米的长方体玻璃缸里面盛满水现在把一块石头放进去水溢出120cm立方把石块取走水面下
C8H10中只有4种属于芳香烃的同分异构体 怎么理解
I think ___ dictionary is enough for us students.A.such one B.so a C.one such D.a so
© 2024 79432.Com All Rights Reserved.
电脑版
|
手机版