若数列{an}是首项为1，公比为a-32的无穷等比数列，且{an}各项的

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问题填空题

若数列{a_n}是首项为1，公比为a-

的无穷等比数列，且{a_n}各项的和为a，则a的值是______．

答案

由题意知a₁=1，q=a-

，且|q|＜1，

∴S_n=

1-q

=a，即

1-a+

= a，

解得a=2．

故答案为2．

填空题

根据句意及首字母提示填单词

1. I have b__________ at 7:00 in the morning.

2. I like salad for l__________.

3. They like c__________, but they don't like beef.

4. She doesn't like i__________ cream.

5. The girl likes eating d__________.

6. He can r__________ fast(快地)．

7. There are some v__________ on the desk.

8. Let's have French f__________.

9. He does w__________ in class.

10. Your food isn't h__________.

问答题简答题

说明完全预报方法与MOS预报方法的区别