
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
The sum of the first $n$ terms of an arithmetic sequence $\{a_n\}$ is $S_n$. Given $f(x) = \frac{2^x-1}{2^x+1}$, and $f(a_2-2) = \sin \frac{2014\pi}{3}$, $f(a_{2014}-2) = \cos \frac{2015\pi}{6}$, then $S_{2015} = \_\_\_\_\_\_$.

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