Geometry

Question Analysis:
This question applies CPCTC.
The main focus is on finding the corresponding side of a given side in congruent triangles.

Key Concept Explanation:
CPCTC means corresponding parts of congruent triangles are congruent.
When △ABC ≅ △DEF, AB corresponds to DE.

Step - by - Step Solution:
Since △ABC ≅ △DEF, and AB = 4 cm, by CPCTC, the corresponding side DE has the same length. So, DE = 4 cm.

Common Mistakes:
Forgetting the correspondence of sides in congruent triangles.