Let's consider the following situations:
a) line contained in the plane: if a straight r has two distinct points on a plane , then r is contained in this plan:
b) competing line or incident to the plan: we say that the straight line r "stick" the plane or that r and are competitors in P When .
Note: the straight r is reverse to all straight lines that do not pass the point P.
c) line parallel to the plane: if a straight r and a plan have no point in common so the straight line r is parallel to a straight line t contained in the plan ; therefore r // .
In there are infinite parallel, reverse or orthogonal lines to r.
P11) If two distinct planes have a point in common, then their intersection is given by a single line passing through that point.Next: Perpendicularism Between Line and Plane