
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 $f(x) = 3\sin x - \pi x$, for any $x \in \left(0, \frac{\pi}{2}\right)$, consider the following four conclusions:

1. $f''(x) > 0$;
2. $f''(x) < 0$;
3. $f(x) > 0$;
4. $f(x) < 0$,

Among these, the correct ones are __________.

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