Geometry

Question Analysis:
This question is about applying CPCTC to exterior angles of congruent triangles.
The main focus is on understanding that corresponding exterior angles of congruent triangles are congruent.

Key Concept Explanation:
CPCTC states that all corresponding parts of congruent triangles are congruent.
This includes exterior angles.
When △ABC ≅ △DEF, the exterior angle at vertex B in △ABC corresponds to the exterior angle at the corresponding vertex E in △DEF.

Step - by - Step Solution:
Given that △ABC ≅ △DEF.
We know that an exterior angle at vertex B in △ABC is 110°.
By CPCTC, the corresponding exterior angle in △DEF (at the vertex corresponding to B, which is E) has the same measure.
So, the measure of the corresponding exterior angle in △DEF is also 110°.

Common Mistakes:
Forgetting that CPCTC applies to exterior angles as well.
Some students might think that CPCTC...