Two planes that do not intersect are said to be parallel. Two planes specified in Hessian normal form are parallel iff left bracketing bar (n_1)^^·(n_2)^^ right bracketing bar = 1 or (n_1)^^x(n_2)^^ = 0 . Two planes that are not parallel always intersect in a line.

Hessian normal form | parallel | parallel lines | plane | plane-plane intersection