Past exam of the groups and representations course of the University of Oxford 2020 2 b Solution 2026-10-25
There are three complex irreducible representations, because there are three conjugacy classes. Two are the trivial representation and the sign representation : both send to , while they send to and , respectively. These exhaust the one-dimensional representations, since their scalar images must satisfy and , forcing , and then .
The defining two-dimensional matrix representation has characterIts character inner product with itself isso it is an irreducible representation. Directly, the two coordinate lines are the distinct eigenspaces of , and exchanges them, leaving no common invariant line. The sum of squares of irreducible representation dimensions is , proving completeness. In the conjugacy class order of solution, the character table isRepresentatives in this table stand for their full conjugacy classes. This lists all irreducible representations up to equivalence of group representations.