累乘法求数列通项公式,an+1=2^n*an,a1=1

问题描述:

累乘法求数列通项公式,an+1=2^n*an,a1=1

a(n+1)=2^n*ana(n+1)/an = 2^nan/a(n-1)=2^(n-1)an/a1 = (2^1)(2^2)...(2^(n-1))           = 2^[n(n-1)/2]an = 2^[n(n-1)/2]

a(n+1)=2^n*an
a(n+1)/an = 2^n
an/a(n-1)=2^(n-1)
an/a1 = (2^1)(2^2)...(2^(n-1))
= 2^[n(n-1)/2]
an = 2^[n(n-1)/2]

首先将原式转换an+1/an=2^n ① 则还有an/an-1=2^(n-1)an-1/an-2=2^(n-2)…………a2/a1=2^1除①式外,以上等式相乘,可得an/a1=2^(n-1)×2^(n-2)×…………2^1即an=2^(n-1+n-2+n-3+………………1)则有an=2^(n*(n-1)/2...