
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
Consider the Earth as a sphere with radius $R$. Point $A$ is located at $30^{\circ}$N latitude and $20^{\circ}$E longitude, and point $B$ is located at $30^{\circ}$N latitude and $80^{\circ}$E longitude. Find the spherical distance between points $A$ and $B$ \_\_\_\_\_\_ (Express the result using inverse trigonometric functions).

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