
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 arithmetic sequence $\{a\_n\}$ with the first term $a\_2=5$, and the sum of the first 4 terms $S\_4=28$.

(I) Find the general term formula of the sequence;

(II) If $b\_n=(-1)^n a\_n$, find the sum of the first $2n$ terms of the sequence $\{b\_n\}$, denoted as $T\_{2n}$.

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