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Let R be the relation on Z≥ (the set of integers) defined by (x, y) ∈ R iff x2 + y2 = 2k for some integers k ≥0.R is not antisymmetric.Which of the following ordered pairs can be used together in a counterexample to prove that R is not antisymmetric? (Remember that R is defined on Z≥)a.(–1, 1) and (1, –1)b.(5, 9) and (13, 15)c.(8, 7) and (7, 8)d.(3, 1) and (1, 3)

Question

Let R be the relation on Z≥ (the set of integers) defined by (x, y) ∈ R iff x2 + y2 = 2k for some integers k ≥0.R is not antisymmetric.Which of the following ordered pairs can be used together in a counterexample to prove that R is not antisymmetric? (Remember that R is defined on Z≥)a.(–1, 1) and (1, –1)b.(5, 9) and (13, 15)c.(8, 7) and (7, 8)d.(3, 1) and (1, 3)

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Solution

The relation R is defined on Z≥, which means it is defined on the set of non-negative integers. Therefore, any pair that includes a negative integer cannot be used as a counterexample to prove that R is not antisymmetric. This rules out option a.

For a relation to be antisymmetric, if (x, y) ∈ R and (y, x) ∈ R, then x must equal y. Therefore, we are looking for a pair of numbers (x, y) such that x² + y² = 2k and y² + x² = 2k, but x ≠ y.

Option b. (5, 9) and (13, 15) cannot be used as a counterexample because 5² + 9² ≠ 2k and 13² + 15² ≠ 2k for any integer k ≥ 0.

Option c. (8, 7) and (7, 8) can be used as a counterexample. Here, 8² + 7² = 2k and 7² + 8² = 2k for some integer k ≥ 0, but 8 ≠ 7. Therefore, this pair can be used to prove that R is not antisymmetric.

Option d. (3, 1) and (1, 3) cannot be used as a counterexample because 3² + 1² ≠ 2k and 1² + 3² ≠ 2k for any integer k ≥ 0.

So, the correct answer is option c. (8, 7) and (7, 8).

This problem has been solved

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