已知数列(an)满足:a1-1,a2-a(a>0),数列(bn)满足bn=ana(n+1)(n∈N)
问题描述:
已知数列(an)满足:a1-1,a2-a(a>0),数列(bn)满足bn=ana(n+1)(n∈N)
(1)若数列(an)是等差数列,且b3=12,求a的值及(an)的通项公式
(2)若(an)是等比数列,求(bn)的前项和Sn
答
题目应该是a1=1,a2=a.没错吧?!(1)若为等差数列,公差为a-1,b3=a3*a4 (用等差数列通项公式写出)被b3=12=[(1+2(a-1))*(1+3(a-1))]化简:6a²-7a-10=0a=2或a=-5/6(a>0 ,舍)所以an=1+1*(n-1)=n(2当a≠1时,公比q=...