已知等差数列｛an｝满足a2=3,a5=9,若数列｛bn｝满足b1=3,bn-1=a下标bn则bn为?
问题描述：
已知等差数列｛an｝满足a2=3,a5=9,若数列｛bn｝满足b1=3,bn-1=a下标bn则bn为?
答
bn-1里的n-1也是下标吧?d=(a5-a2)/3=2an=a2+(n-2)d=2n-1∴a(bn)=2bn - 1又∵b(n-1)=a(bn)∴2bn - 1=b(n-1)2(bn - 1)=b(n-1) - 1∴bn - 1=[b(n-1) - 1]/2∴数列{bn - 1}是以b1 - 1=2为首项,1/2为公比的等比数列.(注：...