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456.02
The icosahedron's five-triangled vertexes have odd-number-imposed,
inherent interangle bisectioning, that is, extensions
of the 30 great circle edges of any of
the icosahedron's 20 triangles automatically bisecting
the apex angle of the adjacently
intruded triangle into which it has passed. Thus extension
of all the icosahedron's 20
triangles' 30 edges automatically bisects all of its
original 60 vertexial-centered,
equiangled 36-degree corners, with all the angle bisectors
inherently impinging
perpendicularly upon the opposite mid-edges of the icosahedron's
20 equilateral,
equiangled 72-degreecornered triangles. The bisecting
great-circle extensions from each of
all three of the original 20 triangles' apexes cross
inherently (as proven elsewhere in
Euclidian geometry) at the areal center of those 20
original icosahedral triangles. Those
perpendicular bisectors subdivide each of the original
20 equiangled triangles into six
right-angled triangles, which multiplies the total surface
subdivisioning into 120 "similar"
right-angled triangles, 60 of which are positive and
60 of which are negative, whose
corners in the spherical great-circle patterning are
90°, 60°, and 36°, respectively, and
their chordally composed corresponding planar polyhedral
triangles are 90, 60, and 30
degrees, respectively. There is exactly 6 degrees of
"spherical excess," as it is formally
known, between the 120 spherical vs. 120 planar triangles.
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