[填空题]
$\text { The table shows the first four terms of three sequences: } u_{n}, v_{n} \text {, and } w_{n} \text {. }$
1. State which sequence is
$u_{n}$ is A $v_{n}$ is B $w_{n}$ is C
1. arithmetic; =
2. geometric. =
2. Find the sum of the first 50 terms of the arithmetic sequence.
3 . Find the exact value of the 13 th term of the geometric sequence.
