I got this question with the image. I am not sure about it. They have also given me an example
Questions on three dimensional geometry sometimes require the student to consider a
two-dimensional representation of the underlying object and use methods of plane
geometry to arrive at the solution. Here is one such example.
Example: An ant lives on the surface of a regular tetrahedron with edges of length 3cm.
It is currently at the midpoint of one of the edges and has to travel to the midpoint of the
opposite edge where a grain is located (see figure). What is the length (in cm) of the
shortest route to the destination assuming that the ant can only travel along the surface
of the tetrahedron?
Solution: The ant has several routes by which it can reach the grain. For instance, it can
travel to the vertex C and move along edge CD.
The idea behind finding the shortest route is to embed the surface of the tetrahedron on
a plane. This is done by opening the tetrahedron along some edges and spreading it out.
For example, the figure on the right is a planar representation containing the triangular
faces ABC and ACD. Notice that ABCD is a rhombus of length 3cm and the segment
joining ant and grain (which is the shortest route) is parallel to the base and thus of
length 3cm as well.
Now use the same idea to solve the problem below where the tetrahedron is replaced by
a cube.
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