The ASA theorem can be used to prove that ΔSEA is congruent to ΔPEN. Looking at the picture, we can see that we are already given that the triangles have one segment and one angle that are congruent. But, we can also see a vertical angle. The two angles that are vertical to each other in this picture are <SEA and <PEN. In addition, by using the Vertical Angles theorem, we know that these two angles are congruent.
Now, we know that the triangles share two angles and one side, meaning that they are congruent by the ASA congruency rule.
