Question

设数列{a n }为等比数列，公比q=2，则 a 2 +3 a 4 +5 a 7 a 4 +3 a 6 +5 a 9 的

Answer 1

∵q=2，

∴

a 2 +3 a 4 +5 a 7

a 4 +3 a 6 +5 a 9 =

a 1 q+3 a 1 q 3 +5 a 1 q 6

a 1 q 3 +3 a 1 q 5 +5 a 1 q 8

=

a 1 q+3 a 1 q 3 +5 a 1 q 6

q 2 (a 1 q+3 a 1 q 3 +5 a 1 q 6 ) =

1

q 2 =

1

4 ．

故答案为：

1

4 ．