问题
选择题
已知等比数列{an}的公比为-
|
答案
∵等比数列{an}的公比为-
，1 4
∴a1+a3+a5+…+a2n-1 a3+a5+a7+…+a2n+1
=a1[1-(
)n]1 16 1- 1 16
a1[1-(1 16
)n]1 16 1- 1 16
=16．
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已知等比数列{an}的公比为-
|
∵等比数列{an}的公比为-
，1 4
∴a1+a3+a5+…+a2n-1 a3+a5+a7+…+a2n+1
=a1[1-(
)n]1 16 1- 1 16
a1[1-(1 16
)n]1 16 1- 1 16
=16．
| 完形填空。 | ||||
| In China, most people's names have 1 parts, the family names and the 2 names. Most people may each have many names. For example, when they are very 3 at home, they usually have nicknames (昵称). At school, they use their 4 names. If someone is a writer, he or she has a 5 name. Now new couples (夫妇) are very 6 when they name their children. Most of the names have 7 meanings. Some show their parents' 8 .Girls' names show that their parents want them to be beautiful and nice. 9 names often show their parents want them to be strong; and 10 to the country. | ||||
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