Questions tagged [3d]
For things related to 3 dimensions. For geometry of 3-dimensional solids, please use instead (solid-geometry). For non-planar geometry, but otherwise agnostic of dimensions, perhaps (euclidean-geometry) or (analytic-geometry) should also be considered.
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Hyperbolic geometry. 3 dimensions. What is not well understood?
According to Mathworld, hyperbolic geometry is well understood in 2 dimensions but not in 3 dimensions.
http://mathworld.wolfram.com/HyperbolicGeometry.html
What isn't well understood about ...
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Why is the volume of a cone one third of the volume of a cylinder?
The volume of a cone with height $h$ and radius $r$ is $\frac{1}{3} \pi r^2 h$, which is exactly one third the volume of the smallest cylinder that it fits inside.
This can be proved easily by ...
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