Theorem 4:   Two intersecting lines are contained in exactly one plane.

1.    Lines l and k intersect at point P.                          1.   Given

2.    l contains at least 2 points, A and P.                      2.    Postulate 1.

3.    k contains at least 2 points, B and P.                     3.    Postulate 1.

4.    P, A, and B are noncollinear.                                  4.    Definition of noncollinear.

5.    P, A, and B are in exactly one plane, m.                5.    Postulate 2.

6.   Lines l and k are in plane m.                                    6.     Postulate 3.

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