数列｛an｝中,a1＝2,a2=3,且｛anan+1｝是以3为公比的等比数列,若bn=2a2n-1+a2n(n为正整数)
问题描述：
数列｛an｝中,a1＝2,a2=3,且｛anan+1｝是以3为公比的等比数列,若bn=2a2n-1+a2n(n为正整数)
a3 a4 a5 a6 都等于多少
答
{a(n)a(n+1)}是首项为a(1)a(2)=6,公比为3的等比数列.a(n)a(n+1)=6*3^(n-1) =2*3^n.a(2n-1)a(2n)=2*3^(2n-1),a(2n)a(2n+1)=2*3^(2n).a(2n+1)/a(2n-1) = [a(2n)a(2n+1)]/[a(2n-1)a(2n)] = [2*3^(2n)]/[2*3^(2n-1)] = 3...