Answer: SAS similarity theorem
Explanation:
Given:

Now from the given figure it can be seen that in ΔXYZ and ΔVWZ
∠WZY=∠WZY [Vertically opposite angles are equal]
Also,

Therefore by SAS criteria of similarity, ΔXYZ and ΔVWZ are similar triangles.
- SAS similarity theorem says that if an angle of a triangle is equal to an angle of a another triangle and the lengths of the sides including these angles are proportional, then the triangles are similar.