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प्रश्न
Let A = {1, 2, 3}. Then number of equivalence relations containing (1, 2) is ______.
विकल्प
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उत्तर
Let A = {1, 2, 3}. Then number of equivalence relations containing (1, 2) is 2.
Explanation:
It is given that A = {1, 2, 3}.
The smallest equivalence relation containing (1, 2) is given by,
R1 = {(1, 1), (2, 2), (3, 3), (1, 2), (2, 1)}
Now, we are left with only four pairs i.e., (2, 3), (3, 2), (1, 3) and (3, 1).
If we odd any one pair [say (2, 3)] to R1, then for symmetry we must add (3, 2). Also, for transitivity we are required to add (1, 3) and (3, 1).
Hence, the only equivalence relation (bigger than R1) is the universal relation.
This shows that the total number of equivalence relations containing (1, 2) is two.
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