等比数列﹛an﹜中,a1=a,前n项和为sn,若﹛an+1﹜成等差数列,求sn?需要详解
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![等比数列﹛an﹜中,a1=a,前n项和为sn,若﹛an+1﹜成等差数列,求sn?需要详解](/uploads/image/z/3970628-44-8.jpg?t=%E7%AD%89%E6%AF%94%E6%95%B0%E5%88%97%EF%B9%9Ban%EF%B9%9C%E4%B8%AD%2Ca1%3Da%2C%E5%89%8Dn%E9%A1%B9%E5%92%8C%E4%B8%BAsn%2C%E8%8B%A5%EF%B9%9Ban%2B1%EF%B9%9C%E6%88%90%E7%AD%89%E5%B7%AE%E6%95%B0%E5%88%97%2C%E6%B1%82sn%3F%E9%9C%80%E8%A6%81%E8%AF%A6%E8%A7%A3)
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等比数列﹛an﹜中,a1=a,前n项和为sn,若﹛an+1﹜成等差数列,求sn?需要详解
等比数列﹛an﹜中,a1=a,前n项和为sn,若﹛an+1﹜成等差数列,求sn?
需要详解
等比数列﹛an﹜中,a1=a,前n项和为sn,若﹛an+1﹜成等差数列,求sn?需要详解
a1=a,等比=d
b1=a+1,等差=k
a2=a*d
b2=a*d+1=a+1+k
a3=a*d*d
b3=a*d*d+1=a+1+2k
a*d*d=a+2k;
a*d=a+k
(a+k)^2=a^2+2ka+k^2=(a+2k)a
k=0,
d=1
sn=n*a