在等比数列 { a n }中, a n >0(n∈ N * ),且 a 6 - a 4 =24, a 3 a 5 =64 ,

2025-05-15 09:34:31
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回答1:

∵a 6 -a 4 =24,a 3 a 5 =64,
∴a 1 ?q 5 -a 1 ?q 3 =24   ①
a 1 q 2 ?a 1 q 4 =64 ②,
解得a 1 =1,q=2或a 1 =-1,q=-2(舍去)  
∴S 8 =
1×(1- 2 8 )
1-2
=255.
故答案为:255