一道,数列题,
来源:学生作业帮 编辑:搜搜考试网作业帮 分类:数学作业 时间:2024/08/19 10:55:10
一道,数列题,
![](http://img.wesiedu.com/upload/c/71/c718ce81964a7aa03936eab661d4b80b.jpg)
![](http://img.wesiedu.com/upload/c/71/c718ce81964a7aa03936eab661d4b80b.jpg)
![一道,数列题,](/uploads/image/z/18958298-50-8.jpg?t=%E4%B8%80%E9%81%93%2C%E6%95%B0%E5%88%97%E9%A2%98%2C)
a1=1/2
7a(n+1) = 3an -5n+6
a(n+1) + (5/4)(n+1) -59/16= (3/7)( an + (5/4)n -59/16)
{an + (5/4)n -59/16}是等比数列,q=3/7
an + (5/4)n -59/16 = (3/7)^(n-1) .(a1 + 5/4 -59/16)
=-(31/16).(3/7)^(n-1)
an =- (5/4)n +59/16 -(31/16).(3/7)^(n-1)
再问: 请问5/4是怎么来的
再答: 7a(n+1) = 3an -5n+6
a(n+1) = (3/7)an - (5/7)n +6/7
let
a(n+1) + k1(n+1) +k2= (3/7)( an + k1n +k2)
coef. of n
-(4/7)k1 = -5/7
k1= 5/4
coef. of constant
-(4/7)k2 -5/4 = 6/7
k2=-59/16
7a(n+1) = 3an -5n+6
a(n+1) + (5/4)(n+1) -59/16= (3/7)( an + (5/4)n -59/16)
{an + (5/4)n -59/16}是等比数列,q=3/7
an + (5/4)n -59/16 = (3/7)^(n-1) .(a1 + 5/4 -59/16)
=-(31/16).(3/7)^(n-1)
an =- (5/4)n +59/16 -(31/16).(3/7)^(n-1)
再问: 请问5/4是怎么来的
再答: 7a(n+1) = 3an -5n+6
a(n+1) = (3/7)an - (5/7)n +6/7
let
a(n+1) + k1(n+1) +k2= (3/7)( an + k1n +k2)
coef. of n
-(4/7)k1 = -5/7
k1= 5/4
coef. of constant
-(4/7)k2 -5/4 = 6/7
k2=-59/16