Comprehesion-I
Let k be the length of any edge of a regular tetrahedron (all edges are equal in length). The angle between a line and a plane is equal to the complement of the angle between the line and the normal to the plane whereas the angle between two plane is equal to the angle between the normals. Let O be the origin and A,B and C vertices with position vectors `veca,vecb` and `vecc` respectively of the regular tetrahedron.
The angle between any two faces is