Equivalence class practice question

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The lesson presents a discrete mathematics practice question on equivalence relations and partitions. The instructor states that A = {1, 2, 3, 4, 5} has partitions {1, 4} and {2, 3, 5}, then asks for the equivalence relation from which these partitions are created. The method shown is to build the relation by listing ordered pairs inside each block of the partition: elements in the same part are related to one another, including reflexive pairs. For {1, 4}, the visible construction begins with pairs such as (1,1), (1,4), (4,1), and (4,4); for {2, 3, 5}, it continues with pairs among 2, 3, and 5. The instructional point is that a partition determines an equivalence relation whose classes are exactly the given blocks, so the answer should contain all ordered pairs needed to make each block closed under reflexivity, symmetry, and transitivity.

Chapters

1. 0:00 – 1:00 00:00-01:00

   This one-minute window presents an equivalence-class practice question. The on-screen prompt states: “Let A = {1, 2, 3, 4, 5} is a set having partitions as {1, 4}, {2, 3, 5}.” It asks for the equivalence relation from which these partitions are created. The instructor writes the set and its two blocks on the board, then begins constructing the relation by listing ordered pairs inside each block. The first block {1, 4} yields pairs (1,1), (1,4), (4,1), and (4,4). The second block {2,3,5} yields pairs among 2, 3, and 5. The lesson emphasizes that an equivalence relation is the union of all ordered pairs whose elements lie in the same partition block.

Teaching progression: first identify the set and partition blocks; second translate each block into ordered pairs; third combine those pairs to form the full relation. This segment can answer doubts such as why (1,4) and (4,1) both appear, why reflexive pairs like (2,2), (3,3), and (5,5) are required, why no pair such as (1,2) is included, and how to verify reflexivity, symmetry, and transitivity from the partition. The expected answer is the union of all pairs inside {1, 4} and all pairs inside {2, 3, 5}, not merely the non-reflexive cross-pairs.