15. If G is a group under the stated operation, prove it; if not, give a...

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15. If G is a group under the stated operation, prove it; if not, give a counterexample: (a) G = Q; a *b =a+b+3 (b) G= {rQ[r 0}; a * b = ab/3 (c) G={rQ[r1}; a * b = a+b+ab 15. If G is a group under the stated operation, prove it; if not, give a counterexample: (a) G = Q; a *b =a+b+3 (b) G= {rQ[r 0}; a * b = ab/3 (c) G={rQ[r1}; a * b = a+b+ab