
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 an arithmetic sequence $\{a_n\}$ satisfies: $a_3=7$, $a_5+a_7=26$. The sum of the first $n$ terms of $\{a_n\}$ is $S_n$.

(Ⅰ) Find $a_n$ and $S_n$;

(Ⅱ) Let $b_n=\frac{1}{a_n^2-1}$ ($n\in N^+$), find the sum of the first $n$ terms of $\{b_n\}$, denoted as $T_n$.

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