Groups \(A\), \(B\), \(C\) and \(D\) are defined as follows:
\(A\): the set of numbers \(\{2, 4, 6, 8\}\) under multiplication modulo 10,
\(B\): the set of numbers \(\{1, 5, 7, 11\}\) under multiplication modulo 12,
\(C\): the set of numbers \(\{2^0, 2^1, 2^2, 2^3\}\) under multiplication modulo 15,
\(D\): the set of numbers \(\left\{\frac{1+2m}{1+2n}, \text{ where } m \text{ and } n \text{ are integers}\right\}\) under multiplication.
- Write down the identity element for each of groups \(A\), \(B\), \(C\) and \(D\). [2]
- Determine in each case whether the groups
\(A\) and \(B\),
\(B\) and \(C\),
\(A\) and \(C\)
are isomorphic or non-isomorphic. Give sufficient reasons for your answers. [5] - Prove the closure property for group \(D\). [4]
- Elements of the set \(\left\{\frac{1+2m}{1+2n}, \text{ where } m \text{ and } n \text{ are integers}\right\}\) are combined under addition. State which of the four basic group properties are not satisfied. (Justification is not required.) [2]