
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 an arithmetic sequence $\{a\_n\}$ with first term $a\_1 (a\_1 \neq 0)$, common difference $d$, and the sum of the first $n$ terms $S_n$. It is known that $a\_1S\_5 + 15 = 0$. Determine the range of values for the real number $d$.

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