2. Let X = {1, 2, 3, 4}.
(a) Write down all the permutations of X as (2 × 4)-matrices.
(b) Which of these permutations are symmetries of the square with vertices 1, 2, 3 and 4?
For each one that is a symmetry, give it the name ρi (for a suitable choice of i) if it is a rotation and σj (for a suitable choice of j) if it is a reflection.
(c) Using your answers to part (b), construct the Cayley table for the dihedral group D4.
(d) Find all subgroups of D4.
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