“微信扫一扫”进入题库练习及模拟考试
在等比数列
参考答案:\(\frac{1}{3}\)
解析:
由题意可得
{{a_1} - {a_2} + {a_3} - {a_4} + {a_5} - {a_6} + {a_7} - {a_8} + {a_9} - {a_{10}} = 5} \\\
{{a_1} + {a_2} + {a_3} + {a_4} + {a_5} + {a_6} + {a_7} + {a_8} + {a_9} + {a_{10}} = 10}
\end{array}} \right.\)
得
{{a_1} + {a_3} + {a_5} + {a_7} + {a_9} = \frac{{15}}{2}} \\\
{{a_2} + {a_4} + {a_6} + {a_8} + {a_{10}} = \frac{5}{2}}
\end{array}} \right.\)
由连比定理得