[填空题]
Only one of the following four sequences is arithmetic and only onebh4hc9 n g2v0v of them is g0gb vc 9vh4hn2; k9xxvkr +uig/e;)d 4g*lk vjeometrij;x*kv9;xe+ur4dgl kg/ v)ki 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$_n$= .
