| A | B |
|---|
| Theorem 3-1 | If two parallel planes are cut by a third plane, then the lines of intersection are parallel. |
| Theoroem 3-2 | If two parallel lines are cut by a transversal, then the alternate interior angles are congruent. |
| Theorem 3-3 | If two parallel lines are cut by a transversal, then the same side interior angles are supplementary. |
| Theroem 3-4 | If a transversal is perpendicular to one of two parallel lines, then it is perpendicular to the other one also.n |
| Theorem 3-5 | If two lines are cut by a transversal and the alternate interior angles are congruent, then the lines are parallel. |
| Theorem 3-6 | If two lines are cut by a transversal and the same side interior angles are supplementary, then the lines are parallel. |
| Theorem 3-7 | In a plane, two lines perpendicular to the same line are parallel. |
| Theorem 3-8 | Through a point outside a line, there is exactly one line parallel to a given line. |
| Theorem 3-9 | Through a point outside a line, there is exactly one line perpendicular to the given line. |
| Theorem 3-10 | Two lines parallel to a third line, are parallel to each other. |
| Theorem 3-11 | The sum of the measures of the angles of a triangle is 180. |
| Theorem 3-12 | The measure of an exterior angle of a triangle equals the sum of the measures of the two remote interior angles. |
| Postulate 10 | If two parallel lines are cut by a transversal, then corresponding angles are congruent. |
| Postulate 11 | If two lines are cut by a transversal and corresponding angles are congruent, then the lines are parallel. |
