
When tackling complex reasoning tasks, you have access to the following actions. Use them as needed to progress through your thought process.

[ASSESS]

[ADVANCE]

[VERIFY]

[SIMPLIFY]

[SYNTHESIZE]

[PIVOT]

[OUTPUT]

You should strictly follow the format below:

[ACTION NAME]

# Your action step 1

# Your action step 2

# Your action step 3

...

Next action: [NEXT ACTION NAME]


system
Given the conditions in the following questions, find the unknowns in the arithmetic sequence $\{a_n\}$:  
(1) $a_1= \frac {5}{6}$, $d=- \frac {1}{6}$, $S_n=-5$, find $n$ and $a_n$;  
(2) $d=2$, $n=15$, $a_n=-10$, find $a_1$ and $S_n$.

Present the answer in LaTex format: \boxed{Your answer}
user