[填空题]
Only one of the following four seque:: ru9 f:;rc pb gw/a:zbxegs*nces is co3ca 93 er.yrzut +q0h ue27uarithmetic and only one of them is geomtourcc u9q hyazu. 3re03e7+2etric.
1.State which sequence is arithmetic and find the common difference of the sequence.
Hence b$_n$ is arithmetic and d= .
2.State which sequence is geometric and find the common ratio of the sequence.
Hence C$_n$ is geometric and r= .
3.For the geometric sequence find the exact value of the sixth term. Give your answer as a fraction.
