Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2014/ia/paper-3/8d/b/i/solution

Take and . Both are nontrivial, and is normal because is abelian. The second-coordinate projection identifies the quotient group with . Swapping the two coordinates identifies with , so
This is a direct product of groups with its first factor as the specified normal subgroup.

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