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# Walking around the world?

Assume for this problem that the earth is a perfect sphere. A point $$P$$ on it's surface has the following property. Starting from $$P$$, suppose you travel $$1$$ mile south, then $$1$$ mile west and finally $$1$$ mile north. Doing so takes you back to the same point $$P$$. Are there any such points $$P$$ other than the north pole? Choose the appropriate option:

• There are no such points.

• Such points for a single circle.

• Such points form at least two but finitely many circles.

• Such points form infinitely many distinct circles.

Note by Paramjit Singh
2 years, 11 months ago

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"Such points can form infinitely many distinct circles", because one can start at a point that is 1 + x miles from the South pole, travel 1 mile south to a distance x from the South Pole, such that in travelling west 1 mile one can end up making n number of circuits coming back to exactly where one was before travelling west, and thence travel 1 mile north back to the point of beginning P. n can be any integer. · 2 years, 11 months ago

x = 1 / 2πn, where n is any integer > 0. Then n circuits or trips around will bring him back to the point where he began traveling west. · 2 years, 11 months ago

Can you clarify what you mean by "making n number of circuits"? · 2 years, 11 months ago

There are no such points. · 2 years, 11 months ago