[填空题]
Only one of the following h ;a*x3 og9nafxqhfwl 5yu,b,c7 6)f cfour sequences is arithmetic and only one of them is geometr fxlu, 5bc,fy wh)6c7qic.
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$_n$= .
