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    Z is set of integers, <Z, ∗> forms group if ∗ is: 
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    Z is set of integers, <Z, ∗> forms group if ∗ is: 

    A.

    ∗(a, b) = a  + b + 2

    B.

    ∗(a, b) = 2a + b

    C.

    ∗(a, b) = (a + b)/2

    D.

    ∗(a, b) = a2 + b

    Correct option is A



    Since it fails the associativity test, it cannot form a group.

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