
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 $f(x)=\frac{1}{2}{{x}^{2}}+ax-(a+1)\ln x\ (a < -1)$, and the tangent line to the function at $x=2$ is parallel to the $x$-axis.

(1) Find the value of $a$;

(2) Find the extreme values of the function $f(x)$.

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