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Define * on Z by a * b = a – b + ab. Show that * is a binary operation on Z which is neither commutative nor associative. |
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Answer» Commutative: Consider two elements 1 and 2 of Z Here, 1 * 2 = 1 – 2 + 1 × 2 = 1 and 2 * 1 = 2 – 1 + 2 × 1 = 3 Therefore, the operation is not commutative. Associative: Take 2, 3, 4 ∈ Z We get (2 * 3) * 4 = (2 – 3 + 2 × 3) * 4 = 5 * 4 = 5 – 4 + 5 × 4 = 21 2 * (3 * 4) = 2 * (3 – 4 + 12) = 2 * 11 = 2 – 11 + 2 × 11 = 13 Here, (2 * 3) * 4 ≠ 2 * (3 * 4) Therefore, the operation is not associative. |
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