Question

The figure below shows PQ and RS as parallel lines cut by the transversal XY.



Which fact is used to prove that angles QMN and MNR are congruent?
Answer
If a transversal intersects two parallel lines, the vertical angles are supplementary.
If a transversal intersects two parallel lines, the alternate interior angles are equal.
If two parallel lines are cut by a transversal, the sum of the complementary angles is 180˚.
If two parallel lines are cut by a transversal, the sum of the alternate exterior angles 180˚.

Answer 1

the correct ans is that if the transversal intersects two parallel lines, the alternate interior angles are equal.

Answer 2

http://www.geom.uiuc.edu/~dwiggins/pict17.GIF