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For all a, b ∈ N, we define a * b = a3 + b3. Show that * is commutative but not associative. |
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Answer» let a = 1,b = 2∈N a*b = 13 + 23 = 9 And b*a = 23 + 13 = 9 Hence * is commutative. Let c = 3 (a*b)*c = 9*c = 9 3 + 33 a*(b*c) = a*(23 + 33) = 1*35 = 13 + 353 (a*b)*c ≠ a*(b*c) Hence * is not associative. |
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