The dihedral angle is the angle θ between two planes. The dihedral angle between the planes a_1 x + b_1 y + c_1 z + d_1 | = | 0 a_2 x + b_2 y + c_2 z + d_2 | = | 0 which have normal vectors n_1 = (a_1, b_1, c_1) and n_2 = (a_2, b_2, c_2) is simply given via the dot product of the normals, cos θ | = | (n_1)^^·(n_2)^^ | = | (a_1 a_2 + b_1 b_2 + c_1 c_2)/(sqrt(a_1^2 + b_1^2 + c_1^2)sqrt(a_2^2 + b_2^2 + c_2^2)).

angle | contact angle | Hessian normal form | line-line angle | plane | plane-plane intersection | tetrahedron | trihedron | vertex angle