
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
Write the general term formula for each of the following sequences based on their first few terms:

1. $4$, $6$, $8$, $10$, $…$;

2. $-\dfrac{1}{1×2}$, $\dfrac{1}{2×3}$, $-\dfrac{1}{3×4}$, $\dfrac{1}{4×5}$, $…$;

3. $a$, $b$, $a$, $b$, $a$, $b$, $…$ (where $a$, $b$ are real numbers);

4. $9$, $99$, $999$, $9999$, $…$.

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