Question

已知等差数列{An}中,公差d大于0,其前n项和为Sn,且满足：a2a3=45,a1+a4=14.？

Answer 1

a1+a4=a2+a3=14
a2×a3=45
且d>0
可知a2=5,a3=9
且d=4,a1=1
1.An=a1+(n-1)×d
=4n-3
Sn=a1+n×(n-1)/2×d
=2n^2-2n+1,7,已知等差数列{An}中,公差d大于0,其前n项和为Sn,且满足：a2a3=45,a1+a4=14.
1.求数列{An}的通项公式；2.通过公式Bn=Sn/（n+c）构造一个新的数列{Bn},若{Bn}也是等差数列,求非零常数c3.求f(n)=Bn除以（n+25）Bn+1【n属于N*】的最大值