Pick's theorem: an inspiring formula for polygonal area | Tangente

In 1910, Albert Einstein, then a non-tenured professor at the university of Zurich, accepted a position in Prague, at that time a German city. One of his closest colleagues at the university was the Austro-Hungarian mathematician Georg Pick. According to some accounts, Pick introduced him to differential geometry: beneath his thoroughly phlegmatic exterior, Pick shared the same interest in theory and teaching.

But Pick is best known for a theorem he proved in 1899 about the area of a polygon—a theorem with several elementary proofs that illustrates the notion of mathematical "beauty."

The power of additivity -----------------------