Final answer:
Without additional context for the variables yxz and yaz, a specific geometric postulate or theorem cannot be definitively identified to prove their equality, although possibilities include the ASA postulate or AA similarity theorem.
Step-by-step explanation:
To determine which postulate or theorem can be used to prove that yxz= yaz, we need to consider the context of the variables and the geometric shapes they represent. In the realm of geometry, postulates and theorems are used to establish the relationships between angles and sides of shapes. If yxz and yaz are angles within the same geometric figure, such as a triangle, and 'y' represents a point that is shared by the two angles yxz and yaz, then it's possible that some version of the Angle-Side-Angle (ASA) postulate or the Angle-Angle (AA) similarity theorem could apply if there are other congruent angles or if the sides affected by 'z' and 'a' are in proportional lengths. However, without a clear diagram or additional information about the relationship between 'x', 'y', 'z', and 'a', it's challenging to provide a specific postulate or theorem. In general, understanding and applying geometric postulates and theorems requires logical reasoning and careful analysis of the parts of a figure to determine how they relate to each other. This logic stems from the same foundational principles as deductive inferences and valid deductive reasoning.