
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 \( x, y \in \left[-\frac{\pi}{4}, \frac{\pi}{4}\right] \), \( a \in \mathbf{R} \), and the equations \( x^3 + \sin x - 2a = 0 \) and \( 4y^3 + \sin y \cos y + a = 0 \), find \( \cos(x + 2y) = \quad \).

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