The points with one line are already proven to be congruent. The points with two lines are already proven congruent. The point in the middle, let’s just call it B. Both triangles are on the vertical line of B, which I will call AC (therefore being line ABC). The horizontal line will be called DBE. Both triangles share point B. Since DBE intercepts ABC, those two angles must be congruent.
You could also say that since there are already two confirmed congruent angles, the the third pair of angles must be congruent in order for both of the triangles to be actual triangles.
