Assertion: tetrahedron's angle | /r/CapableOf | sum to one hundred and eighty degrees
Facets:
Source sentences:
text: Since each vertex is thus effectively formed by three different internal angles from triangles that are congruent, and since the three internal angles of a triangle always add up to one hundred and eighty degrees (180°), then the face angles at each vertex of an isosceles tetrahedron must also sum to one hundred and eighty degrees.