高一数学在线急.. 已知数列{an}满足a1=1,a(n+1)-2an=2^n,求an
问题描述:
高一数学在线急.. 已知数列{an}满足a1=1,a(n+1)-2an=2^n,求an
1,已知数列{an}满足a1=1,a(n+1)-2an=2^n,求an
2,已知数列{an}满足a(n+1)=2an-3,求an
3,求数列2-1,2^2-2,2^3-3,...,2^n-n,的前n项和
三道题求过程,分不多了...
答
a(n+1)-2an=2^na(n+1)=2an+2^n两边同时除以2^(n+1)a(n+1)/2^(n+1)=an/2^n+1/2设an/2^n为bn则bn+1=bn+1/2累加解得bn=b1+1/2因为a1=1/2解得b1=1/2bn=1/2+1/2=1an/2^n=1an=2^n第二题a(n+1)=2an-3a(n+1)-1...