
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 points $F_1$ and $F_2$ are the left and right foci, respectively, of the ellipse $\dfrac{x^2}{a^2} + \dfrac{y^2}{b^2} = 1$. The line passing through $F_1$ and perpendicular to the $x$-axis intersects the ellipse at points $M$ and $N$. If $\triangle MNF_2$ is an isosceles right-angled triangle, find the eccentricity $e$ of the ellipse.

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