
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 the sequence $\{a_n\}$ is an arithmetic sequence, with $a_4 = 15$ and $S_5 = 55$, find the angle of inclination of the line passing through the points $P(4, a_{2010})$ and $Q(3, a_{2011})$. (Express the result using an inverse trigonometric function).

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