[填空题]
Only one of the following four ser: l:s-lu:*.aj vmr ejquences is arithr 0 p5- tsa2-p8q y0i rdrnf);:oadbrrmetic and only one of them is geometridaq0p2;r0)rrb yr-po: rsi a 5td8fn-c.
1.State which sequence is arithmetic and find the common difference of the sequence.
Hence C$_n$ is arithmetic and d= .
2.State which sequence is geometric and find the common ratio of the sequence.
Hence d$_n$ is geometric and r= .
3.For the geometric sequence find the exact value of the eighth term. Give your answer as a fraction.
Using the nth term formula d$_n$= .
