Answer
SAS theorem
Work Step by Step
In this diagram, we see that one side of each triangle is marked congruent. Additionally, one side is shared by both triangles; therefore, this side is congruent. The included angle between these two sides are right angles, and right angles are congruent to one another.
Now, we have two sides and an included angle that are congruent. Therefore, we can use the SAS theorem to prove the triangles are congruent.
