
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
At the vertices of a square with side length \( a \) are located four charges: \( q, q, q, -q \). What are the magnitude of the electric field \( E \) and the electric potential \( \varphi \) at the midpoint of the side of the square that connects the positive and negative charges?

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