Homework Help: Algebra problem: walking on the surface of the earth (check if answer is correct)

1. Mar 25, 2012

analyzer

1. The problem statement, all variables and given/known data
Arnoldo Téllez walked one mile to the south, then one mile to the east, and then one mile to the north, getting back to the point where he started. He could have started in the north pole, but he didn't. Where did he start?
(Taken from ALGEBRA AND TRIGONOMETRY WITH ANALYTIC GEOMETRY: A PROBLEM-SOLVING APPROACH, by Varberg and Fleming.)

2. Relevant equations

3. The attempt at a solution
He could have started at several different points:
- At any of the points that are one mile to the north from the parallel whose length is one mile (if that parallel exists).
- At any of the points that are one mile to the north from the parallel whose length is one half of a mile (if that parallel exists), thus walking twice over that parallel.
- At any of the points that are one mile to the north from the parallel whose length is one third of a mile (if that parallel exists), thus walking three times over that parallel.
- and so on...

2. Mar 25, 2012

Joffan

Yes. The parallels specified do exist, with points available one mile to the north - where?

3. Mar 25, 2012

analyzer

Where?

Those points must be part of other parallels, respectively.

4. Mar 25, 2012

Joffan

Sorry, I wasn't clear. Where are the parallels of the required length, given that they must also have points one mile to the north?

5. Mar 25, 2012

analyzer

Those parallels must be on the southern hemispere. I don't know exactly where.

6. Mar 25, 2012

Joffan

Where do you find such short parallels?

7. Mar 25, 2012

analyzer

South Pole?

8. Mar 25, 2012

analyzer

Near the South Pole, that is.

9. Mar 25, 2012

Joffan

Correct! Very near the south pole, in fact. You can essentially ignore the curvature of the Earth to get a good approximation of how far they are from the pole...

10. Mar 25, 2012

analyzer

The Antarctic?

11. Mar 25, 2012

analyzer

Arnoldo Téllez could have started at any of the points which are one mile to the north from the parallel which is at 1/(2*pi) miles from the South Pole; i.e. he could have started at any of the points which are (1 + 1/(2*pi)) miles from the South Pole.

12. Mar 25, 2012

analyzer

Right?

13. Mar 27, 2012

Joffan

Sorry analyzer - yes, absolutely correct, for the "once round the pole" version...