# Questions tagged [geometry]

Branch of Mathematics about the properties of the shapes, their similarities and transformations in the space.

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### How old is the idea of an Oscullating Circle? [duplicate]

In the second volume of Spivak's Comprehensive introduction to differential geometry, he begins the discussion of curvature by discussing the oscullating circle of a curve in the plane. This leads me ...
237 views

### Why did Columbus think the Earth was much smaller than it is?

Columbus set off on his westward journey to Asia, believing the Earth was much smaller than it is. There was some apparent disagreement about the size, and Columbus was staking his life on it. Why ...
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### Did the ancients have the concept of dimension?

Plainly, they knew what a circle and sphere were and also a square and cube; but did they discuss the idea that a sphere was analogous to a circle but in 3 dimensions or similarly the analogy between ...
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### Why 360° is assigned to circle full turn ? Not any other number? [duplicate]

Please look at this question https://math.stackexchange.com/posts/comments/9011243?noredirect=1 A user comment this so I thought of asking here You mean why did we decide on using 360 degrees? I don'...
9k views

### What is the etymology behind sine, cosine, tangent, etc.?

I heard somewhere that it was actually a mistake in translation. What's the correct story?
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### What is Ptolemy holding in this picture?

I would like to know the name of the device Ptolemy is holding in the following picture. [Image Source]
126 views

### What is the origin of the "problem of Brahmagupta" of constructing inscribed quadrangle with given sides?

I am looking for a source of the following construction problem: Construct an inscribed quadrangle with given sides. I know it under the name problem of Brahmagupta, but I do not know any evidence ...
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### Where in Gauss's nachlass did he pose the problem of connectedness of a surface?

On p.98 of the book "Mathematics of the 19th Century: Geometry, Analytic Function Theory", the authors mention a note written by Gauss in 1840: In 1840 Gauss wrote a note in which he introduced the ...
208 views

### How did the "Wheel of Theodorus" become known as the "Wheel of Einstein"?

I've desperately searched the Internet, to no avail, to find a citation of how the "Wheel of Theodorus" became known as the "Wheel of Einstein" as claimed by Wikipedia and Wolfram.