
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
Let the function $f(x)$ be a differentiable function defined on $(-\infty, 0)$, with its derivative denoted as $f'(x)$, and it satisfies $3f(x) + xf'(x) < 0$. Find the solution set of the inequality $(x+2016)^3f(x+2016) + 8f(-2) < 0$.

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