求助gwd-13-30

hsu_2008

gwd-13-30: If the the sequence x1, x2, x3,..., xn, ... is such that x1=3 and xn+1=2xn-1 for n>=1, then x20-x19=

A.2^19

B.2^20

C.2^21

D.2^20-1

E.2^21-1

这道题没有搜到讨论的帖子。我做这种sequence的题是完全没有头绪. 求好心人帮忙！谢谢！！！！

buda

xn+1=2xn-1
这个角标能不能写清楚呢？很有歧义呢

fly_holly

If the sequence x₁, x_2, x_{3, …,} x_n, … is such that x₁  = 3 and x_n+1
                    = 2x_n – 1 for n ≥ 1, then x₂₀ – x₁₉ =

 

A.     2¹⁹

B.     2²⁰

C.     2²¹

D.     2²⁰ - 1

E.      2²¹ - 1

fly_holly

如图

fly_holly

[attachimg]67156[/attachimg]

hsu_2008

Thank you,fly_holly ^_^