
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
Chris is located at point $C$ near the Equator in Libreville, Gabon, at coordinates $0^\circ$ latitude and $9^\circ \text{ E}$ longitude. Dana is situated at point $D$ near the Tropic of Cancer in Lhasa, Tibet, at coordinates $30^\circ \text{ N}$ latitude and $91^\circ \text{ E}$ longitude. Assuming that Earth is a perfect sphere with centre $E$. Calculate the degree measure of $\angle CED$.

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