等差数列前n项求和设Sn是等差数列{an}的前n项和,若a5\a3=5\9,则S9\S5=()A.1 B.-1 C.2 D.1\2求详解啊~谢谢
来源:学生作业帮助网 编辑:作业帮 时间:2024/06/20 17:58:52
![等差数列前n项求和设Sn是等差数列{an}的前n项和,若a5\a3=5\9,则S9\S5=()A.1 B.-1 C.2 D.1\2求详解啊~谢谢](/uploads/image/z/3721513-49-3.jpg?t=%E7%AD%89%E5%B7%AE%E6%95%B0%E5%88%97%E5%89%8Dn%E9%A1%B9%E6%B1%82%E5%92%8C%E8%AE%BESn%E6%98%AF%E7%AD%89%E5%B7%AE%E6%95%B0%E5%88%97%7Ban%7D%E7%9A%84%E5%89%8Dn%E9%A1%B9%E5%92%8C%2C%E8%8B%A5a5%5Ca3%3D5%5C9%2C%E5%88%99S9%5CS5%3D%28%29A.1++B.-1++C.2++D.1%5C2%E6%B1%82%E8%AF%A6%E8%A7%A3%E5%95%8A%EF%BD%9E%E8%B0%A2%E8%B0%A2)
等差数列前n项求和设Sn是等差数列{an}的前n项和,若a5\a3=5\9,则S9\S5=()A.1 B.-1 C.2 D.1\2求详解啊~谢谢
等差数列前n项求和
设Sn是等差数列{an}的前n项和,若a5\a3=5\9,则S9\S5=()
A.1 B.-1 C.2 D.1\2
求详解啊~谢谢
等差数列前n项求和设Sn是等差数列{an}的前n项和,若a5\a3=5\9,则S9\S5=()A.1 B.-1 C.2 D.1\2求详解啊~谢谢
S9/S5=((a1+a9)*9)/((a1+a5)*5)=(2*a5*9)/(2*a3*5)=9*a5/5*a3=1
关键2*a5=a1+a9 2*a3=a1+a5
S9/S5=(9a5)/(5a3)=1
选A