问题
选择题
已知数列{an}满足a1=5，anan+1=2n，则
|
答案
∵anan+1=2n，
∴anan-1=2n-1，
∴
=2，an+1 an-1
∴数列{an}的奇数项成等比数列，偶数项成等比数列；
∴a3=5×2=10，a7=5×23=40，故
=a7 a3
=440 10
故答案为 B
搜题请搜索小程序“爱下问搜题”
已知数列{an}满足a1=5，anan+1=2n，则
|
∵anan+1=2n，
∴anan-1=2n-1，
∴
=2，an+1 an-1
∴数列{an}的奇数项成等比数列，偶数项成等比数列；
∴a3=5×2=10，a7=5×23=40，故
=a7 a3
=440 10
故答案为 B
| 阅读理解。 | ||||||||||||
| This is my family. My grandpa's name is Harry Brown. My grandma's name is Jean Brown. My father's name is Jeff Brown. My mother's name is Helen Brown. Jeff and Helen are my parents. I have a sister. Her name is Kate Brown. My name is Tom Brown. I'm ten. My sister is eight. | ||||||||||||
| (A). 阅读短文，将人名及其身份填在表中相应方框内。 | ||||||||||||
| ||||||||||||
| (B). 根据短文内容，回答下列问题。 | ||||||||||||
| 6. How old is Tom Brown? _______________________. 7. Is that girl his sister? _______________________. 8. Is Helen Brown his grandmother? _______________________. 9. What's his grandmother's name? _______________________. 10. Is Jeff Brown his brother? _______________________. |