[填空题]
Only one of the following four sequences is arisu,a*b 0-k jjqfn jo:+thmetic and only onehk+bmc7s 9srk9c y-8:z :jeaq of them is geometric7b -y k:jcq:hz + 9er8sck9mas.
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$_n$= .
