已知{an}是等差数列,且{sn}是{an}的前n项和,a1,a3,a4成等比数列,求(s3-s2)/(s5-s3)的值快
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![已知{an}是等差数列,且{sn}是{an}的前n项和,a1,a3,a4成等比数列,求(s3-s2)/(s5-s3)的值快](/uploads/image/z/2427610-58-0.jpg?t=%E5%B7%B2%E7%9F%A5%7Ban%7D%E6%98%AF%E7%AD%89%E5%B7%AE%E6%95%B0%E5%88%97%2C%E4%B8%94%7Bsn%7D%E6%98%AF%7Ban%7D%E7%9A%84%E5%89%8Dn%E9%A1%B9%E5%92%8C%2Ca1%2Ca3%2Ca4%E6%88%90%E7%AD%89%E6%AF%94%E6%95%B0%E5%88%97%2C%E6%B1%82%28s3-s2%29%2F%28s5-s3%29%E7%9A%84%E5%80%BC%E5%BF%AB)
已知{an}是等差数列,且{sn}是{an}的前n项和,a1,a3,a4成等比数列,求(s3-s2)/(s5-s3)的值快
已知{an}是等差数列,且{sn}是{an}的前n项和,a1,a3,a4成等比数列,求(s3-s2)/(s5-s3)的值
快
已知{an}是等差数列,且{sn}是{an}的前n项和,a1,a3,a4成等比数列,求(s3-s2)/(s5-s3)的值快
a1,a3,a4成等比数列
a3^2=a1*a4
a3^2=(a3-2d)*(a3+d)
a3^2=a3^2-2d^2-d*a3
d*(2d+a3)=0
d1=0
d2=-a3/2
d=0时
(s3-s2)/(s5-s3)
=a3/(a4+a5)
=1/2
d=-a3/2时
(s3-s2)/(s5-s3)
=a3/(a4+a5)
=a3/(2a3-3a3/2)
=1/(1/2)=2
1/2,设一下就搞定了,小题就直接都设为1