问题
填空题
已知an,bn都是等差数列,其前n项和分别是Sn,和Tn,若
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答案
S15=
=(a1+a15)×15 2
=15(a1+7d)=15a8,同理可得T15=15b8(a1+a1+14d)×15 2
则
=a8 b8
=S15 T15
=15-6 2×15-3 1 3
故答案为:1 3
已知an,bn都是等差数列,其前n项和分别是Sn,和Tn,若
|
S15=
=(a1+a15)×15 2
=15(a1+7d)=15a8,同理可得T15=15b8(a1+a1+14d)×15 2
则
=a8 b8
=S15 T15
=15-6 2×15-3 1 3
故答案为:1 3