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MC I-C problem 7.26

 
 
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Re: MC I-C problem 7.26
ReynosoDavid - 2019年01月28日 Monday 12:11
 

You just need to verify it. That is, you will need to count the number of faces ($F$), vertices ($V$), and edges ($E$) of the regular octahedron, and verify that indeed $V - A + F = 2$.

For this purpose a picture is not needed, since we know it is formed by $8$ equilateral triangles. (Think of two square pyramids glued together by their square faces.)