
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 $f(x)=-a\ln x+(a+1)x-\frac{1}{2}x^{2}\;(a > 0)$
(1) If $x=1$ is the maximum point of the function $f(x)$, find the monotonically decreasing interval of the function $f(x)$;
(2) If $f(x)\geqslant -\frac{1}{2}x^{2}+ax+b$ always holds, find the maximum value of the product $ab$ of the real numbers $a$ and $b$.

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