theorems (lines and planes)

Theorem 6-1
--> Two parallel lines lie in exactly one plane

Theorem 6-2
--> In a plane, two lines are parallel if they are both perpendicular at the same line.

Theorem 6-3
--> Let L be a line and let P be a point NOT on L. There is at least one line through P parallel to L.

Theorem 6-4
--> If 2 lines are cut by a transversal and one pair of alternate interior angles are congruent, then the other pair of alternate angles are also congruent.