Let G be a finite group. The center Z(G) of G is defined to be the set of all group elements z E G such that z.g = g·z for all g € G. Show that Z(G) is an abelian subgroup of G.

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ChapterP: Prerequisites: Fundamental Concepts Of Algebra
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Let G be a finite group. The center Z(G) of G is defined to be the set of all group elements
z E G such that
z.g = g ·z for all g € G.
Show that Z(G) is an abelian subgroup of G.
Determine the center of the symmetry group D4 of the square.
Prove that for any complex irreducible representation R of G, if z E Z(G) then R(z) is a scalar
matrix, i.e. R(z) is of the form AI where I is the identity matrix. If z is an elements of order d,
show that this scalar is a complex d-th root of unity.
Hint: Take an eigenvalue A of R(z) and show that for all g e G,
(R(z) – AI) · R(g) = R(g) · (R(z) – AI).
Then use Schur's lemma.
Transcribed Image Text:Let G be a finite group. The center Z(G) of G is defined to be the set of all group elements z E G such that z.g = g ·z for all g € G. Show that Z(G) is an abelian subgroup of G. Determine the center of the symmetry group D4 of the square. Prove that for any complex irreducible representation R of G, if z E Z(G) then R(z) is a scalar matrix, i.e. R(z) is of the form AI where I is the identity matrix. If z is an elements of order d, show that this scalar is a complex d-th root of unity. Hint: Take an eigenvalue A of R(z) and show that for all g e G, (R(z) – AI) · R(g) = R(g) · (R(z) – AI). Then use Schur's lemma.
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