Monthly Archives: March 2011

Probability that the second child is a girl?

Two parents have two children. One of the children (first or second) is a girl. What is the probability that the second child is a girl? Answer: There are 4 possibilities: 1. First boy, second boy. 2. First boy, second … Continue reading

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Air distance

In the last post a proof of the spherical law of cosines was made. For the figure below, following equality holds:   (***) The earth is more like an ellipsoid but for computing the air distance with enough accuracy it … Continue reading

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Cosine theorem on the sphere

The cosine theorem on a sphere is an interesting relation that holds for a spherical triangle. One of it’s main applications is the computation of the air distance between two geographical points given by their latitude – longitude coordinates (I’ll show how … Continue reading

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