
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 ellipse \(\frac{x^{2}}{a^{2}}+\frac{y^{2}}{b^{2}}=1\) with \(a > b > 0\), let \(F_{1}\) be the left focus, \(P\) be the vertex \((0, b)\), and \(AB\) be a chord passing through \(F_{1}\), with \(A\) in the first quadrant (both \(A\) and \(B\) lie on the ellipse). If \(\angle APB = 90^\circ\), find the slope of the line \(AB\).

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