Just like triangles, any tetrahedron has an incenter which is the center of the unique inscribed sphere that touches its four faces, and a circumcenter which is the center of the unique sphere that passes through its four vertices. Given the tetrahedron with vertices find the distance between its incenter and its circumcenter.
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As I showed for the previous question , we can calculate the incentre of the tetrahedron to have coordinates ( 1 7 + 2 3 3 + 2 4 9 + 3 1 3 5 2 3 3 + 1 0 2 4 9 − 5 3 1 3 , 1 7 + 2 3 3 + 2 4 9 + 3 1 3 1 2 2 3 3 + 2 3 1 3 , 1 7 + 2 3 3 + 2 4 9 + 3 1 3 1 7 0 ) The outcentre of the tetrahedron is the point of intersection of the three planes with equations r ⋅ ( a − b ) r ⋅ ( a − c ) r ⋅ ( a − d ) = 2 1 ( ∣ a ∣ 2 − ∣ b ∣ 2 ) = 2 1 ( ∣ a ∣ 2 − ∣ c ∣ 2 ) = 2 1 ( ∣ a ∣ 2 − ∣ d ∣ 2 ) and hence has coordinates ( 3 4 9 9 , 3 4 1 3 9 , 3 4 9 9 ) Thus the distance between the outcentre and the incentre is 1 . 0 8 3 1 7 6 3 6 2 .