Sn等差数列,S3比S6等于1/3,则S6比S7等于多少
1个回答
s3=3(a1+d)
s6=3S3=9(a1+d)=6a1+15d 所以a1=2d
s6=27d
s7=7a1+21d=35d
s6:s7=27:35
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