
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 the function $f(x) = \ln(1+x) - \frac{ax}{1+x}$.  
(I) If $a=2$, find the equation of the tangent line to $f(x)$ at $x=1$.  
(II) If $f(x) \geqslant 0$ holds for all $x \in (-1, +\infty)$, find the range of the real number $a$.

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