
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 $f(x) = 2x^3 - 3(a + 1)x^2 + 6ax + 8$, where $a \in \mathbb{R}$. It is known that $f(x)$ has an extremum at $x = 3$.

(1) Find the explicit formula of $f(x)$;  
(2) Find the equation of the tangent line to $f(x)$ at point $A(1, 16)$.

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