设sn是等差数列前n项和,若s3/s6=1/3则s6/s12=?
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设sn是等差数列前n项和,若s3/s6=1/3则s6/s12=?
答案是3/10
答案是3/10
![设sn是等差数列前n项和,若s3/s6=1/3则s6/s12=?](/uploads/image/z/19316037-21-7.jpg?t=%E8%AE%BEsn%E6%98%AF%E7%AD%89%E5%B7%AE%E6%95%B0%E5%88%97%E5%89%8Dn%E9%A1%B9%E5%92%8C%2C%E8%8B%A5s3%2Fs6%3D1%2F3%E5%88%99s6%2Fs12%3D%3F)
3(a1+a3) 1
----------- = ---
6(a1+a6) 3
所以
a1+a1+2d 2
-------------- = ---
a1+a1+5d 3
解得a1=2d
s6 6(a1+a6) 6(a1+a1+5d) 12a1+30d 54d
---- = -------------- = -------------------- = -------------------- = ------
s12 12(a1+a12) 12(a1+a1+11d) 24a1+132d 180d
3
= -----
10
GOOD LUCK~~~
----------- = ---
6(a1+a6) 3
所以
a1+a1+2d 2
-------------- = ---
a1+a1+5d 3
解得a1=2d
s6 6(a1+a6) 6(a1+a1+5d) 12a1+30d 54d
---- = -------------- = -------------------- = -------------------- = ------
s12 12(a1+a12) 12(a1+a1+11d) 24a1+132d 180d
3
= -----
10
GOOD LUCK~~~
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