
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
In $\triangle ABC$, it is known that the internal angle $A= \dfrac {\pi}{3}$, and the side $BC=2 \sqrt {3}$. Let the internal angle $B=x$, and the area of $\triangle ABC$ be $y$.

(I) Find the analytical expression and domain of the function $y=f(x)$;

(II) For what value of angle $B$ is the area of $\triangle ABC$ maximum.

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