No, △YXZ ≅△AZX is not a valid ASA congruence theorem. ASA stands for Angle-Side-Angle, and it means that two triangles are congruent if they have two pairs of corresponding angles congruent and the included (or corresponding) sides congruent. However, in △YXZ ≅△AZX, we do not have two pairs of corresponding angles congruent.
