Modern Pure Solid Geometry

altitude bimedians centers of similitude centroid circumcenter circumsphere coaxal pencil coincides collinear coplanar Corollary corresponding DABC diagonals diameter dihedral dihedral angle Euler line external bisectors Find the locus four given spheres four lines four spheres given line given point given tetrahedron harmonic conjugate hedron hence the proposition homothetic hyperbolic group internal bisecting planes isoclinal lines isodynamic points isodynamic tetrahedron isogonal isosceles tetrahedron Lemoine point line of centers line of intersection lines joining medians meet mid-point opposite edges opposite faces orthic orthocentric group orthocentric tetrahedron orthogonal sphere pairs of opposite parallel parallelepiped pencil of spheres plane ABC plane determined plane passing point with respect points of contact polar plane radical axis radical plane radii radius ratio respectively opposite S-abc segment skew lines skew quadrilateral sphere of similitude spheres of antisimilitude squares symmedian tangent plane tetrahedron ABCD three lines three spheres triangle ABC trihedral angle trihedron vertex