Y by Adventure10, Mango247
The altitudes
of a tetrahedron
intersect in the center
of the sphere inscribed in the tetrahedron
. Prove that the tetrahedron
is regular.
(D. Tereshin)





(D. Tereshin)
Free webinar 4/3 about Learning with AoPS: Perspectives from a Parent, Math Camp Instructor, and University Professor.
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