回復 14# nanpolend 的帖子
單選第1題
\(\begin{align}
& {{a}_{1}},{{a}_{2}},\cdots ,{{a}_{7}}>0 \\
& {{a}_{8}},{{a}_{9}},\cdots <0 \\
& \left| {{a}_{7}} \right|<\left| {{a}_{8}} \right| \\
& \left| {{a}_{6}} \right|<\left| {{a}_{9}} \right| \\
& \left| {{a}_{5}} \right|<\left| {{a}_{10}} \right| \\
& \left| {{a}_{4}} \right|<\left| {{a}_{11}} \right| \\
& \left| {{a}_{3}} \right|<\left| {{a}_{12}} \right| \\
& \left| {{a}_{2}} \right|<\left| {{a}_{13}} \right| \\
& \left| {{a}_{1}} \right|<\left| {{a}_{14}} \right| \\
\end{align}\)
\(n\ge 14\)時，\({{S}_{n}}<0\)，\(n\)之最大值13
