本题目来源于试卷: Sequences & Series，类别为 IB数学
[问答题]
Only one of the following four sequences is arithmetic and oa w3kxy(gj/0z0s mut zd2ek 5o7qktv7s+35 jjnly one of them is gveo5k3u25t+qsj 7szt 7j 0dmkeometric.
$\begin{aligned}
a_{n} & =\frac{1}{3}, \frac{1}{4}, \frac{1}{5}, \frac{1}{6}, \ldots & c_{n} & =3,1, \frac{1}{3}, \frac{1}{9}, \ldots \\
b_{n} & =2.5,5,7.5,10, \ldots & d_{n} & =1,3,6,10, \ldots
\end{aligned}$
1. State which sequence is arithmetic and find the common difference of the sequence.
2. State which sequence is geometric and find the common ratio of the sequence.
3. For the geometric sequence find the exact value of the sixth term. Give your answer as a fraction.
参考答案: 
本题详细解析:
| 
