设{An}满足前n+1项的和加上前n项的和等于2倍的第n+1项,a1=3,求这个数列的通项式,和前n项的和.
设{An}满足前n+1项的和加上前n项的和等于2倍的第n+1项,a1=3,求这个数列的通项式,和前n项的和.
要有步骤或说明
(答得好有加分)
要有步骤或说明
(答得好有加分)
数学人气:400 ℃时间:2020-04-04 06:25:14
优质解答
S(n+1)+s(n)=2a(n+1);s(n)+s(n-1)=2a(n);上下相减;a(n+1)+a(n)=2a(n+1)-2a(n);所以 a(n+1)=3a(n);即 a(n) 是以a(1)=3为首项,3为公比的等比数列.所以 s(n)=n*a(1)+q*n(n-1)/2=3n+3/2*n(n-1)=3/2*n^2+3/2*nover...
我来回答
类似推荐
猜你喜欢
- 1读书心得50字以下
- 2我真的很喜欢每天晚饭后散步 用英语怎么翻译
- 3the summary of The Merchant of Venice
- 4She likes( )busy.She always has many thinks( )
- 5把 一个正方体切成两个完全相同的长方体后表面积增加了72平方厘米,原来正方体的体积是( )立方厘米
- 6若直线2ax-by+2=0(a>0,b>0)始终平分圆(x+1)2+(y-2)2=4的面积,则ab的最大值等于_.
- 7There are three birthdays in june.译成汉
- 8多么热闹啊用英语怎么说
- 9Once a rich woman asked Martin Brown,a famous singer,to her house.She wanted him to sing for her friends.But she didn't
- 10计算:(3/20+7/50-2/25)÷1/100=?1/2÷【2/3×(6/7-5/14)】=?