The exterior angles of the 12-sided plane polygon called a dodecagon measure 360°/12 = 30°. So the interior angles each measure 180°-30° = 150°.
You asked about a 12-sided 3-dimensional solid dodecahedron. The interior angles of its regular pentagonal faces will have a measure of 108°, just as those of any regular pentagon do. The dihedral angle between the faces is 2*arctan[(1+√5)/2] ≈ 116.565°.
You asked about a 12-sided 3-dimensional solid dodecahedron. The interior angles of its regular pentagonal faces will have a measure of 108°, just as those of any regular pentagon do. The dihedral angle between the faces is 2*arctan[(1+√5)/2] ≈ 116.565°.
