Sn是等差数列前N项和,且S5/S3=9/5 求S9/S5SORRY.说错了.是Sn是等差数列前N项和,且S5/S3=5/9 求S9/S5
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Sn是等差数列前N项和,且S5/S3=9/5 求S9/S5SORRY.说错了.是Sn是等差数列前N项和,且S5/S3=5/9 求S9/S5
Sn是等差数列前N项和,且S5/S3=9/5 求S9/S5
SORRY.说错了.是Sn是等差数列前N项和,且S5/S3=5/9 求S9/S5
Sn是等差数列前N项和,且S5/S3=9/5 求S9/S5SORRY.说错了.是Sn是等差数列前N项和,且S5/S3=5/9 求S9/S5
设Sn=na1+n*(n-1)d
S5=5a1+10d S3=3a1+3d
有25a1+50d=27a1+27d
a1=11.5d
S9=11.5*9d+36d S5=5*11.5d+10d
S9/S5 =31/15
Sn是等差数列前N项和,且S5/S3=9/5 求S9/S5SORRY.说错了.是Sn是等差数列前N项和,且S5/S3=5/9 求S9/S5
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