
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
If the even function $y = f(x)$ is a periodic function with a period of 6 on $\mathbb{R}$, and satisfies $f(x) = (x + 1)(x - a)$ for $-3 \leq x \leq 3$, then $f(-6) =$ \_\_\_\_\_\_.

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