
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 that $\{a_n\}$ is an arithmetic sequence with a common difference not equal to zero, it satisfies $a_3 = 7$, and $a_2$, $a_4$, $a_9$ form a geometric sequence.

(I) Find the general formula for the sequence $\{a_n\}$;

(II) Let sequence $\{b_n\}$ satisfy $b_n=a_n \cdot a_{n+1}$, find the sum of the first $n$ terms, $S_n$, for the sequence $\left\{ \dfrac {1}{b_n} \right\}$.

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