The dihedral angle between planes with normals n_{1} and n_{2} is: cos(theta) = |n_{1}.n_{2}|/(|n_{1}||n_{2}|). Planes are perpendicular when n_{1}.n_{2} = 0. Planes are parallel when n_{1} = kn_{2} (normals are proportional). The distance between parallel planes ax+by+cz = d_{1} and ax+by+cz = d_{2} is |d_{1}-d_{2}|/sqrt($a^{2}$+$b^{2}$+$c^{2}$). Note: ensure the planes have the same normal coefficients before applying the distance formula.