A general linear group over a field is finite if and only if the field is finite
Solution to Abstract Algebra by Dummit & Foote 3rd edition Chapter 1.4 Exercise 1.4.5 Let $F$ be a field. Show that $GL_n(F)$ is a finite group if and only if…
If n is composite, then Z/(n) is not a field
Solution to Abstract Algebra by Dummit & Foote 3rd edition Chapter 1.4 Exercise 1.4.4 Show that if $n$ is not prime, then $\mathbb{Z}/(n)$ is not a field. Solution: If $n$…
Show that a given general linear group is nonabelian
Solution to Abstract Algebra by Dummit & Foote 3rd edition Chapter 1.4 Exercise 1.4.3 Show that $GL_2(\mathbb{F}_2)$ is non-abelian. Solution: We have $$\left[ {1 \atop 1}{1 \atop 0} \right] \cdot…
Compute the order of each element in the general linear group of dimension 2 over Z/(2)
Solution to Abstract Algebra by Dummit & Foote 3rd edition Chapter 1.4 Exercise 1.4.2 Write out all the elements in $GL_2(\mathbb{F}_2)$ and compute the order of each element. Solution: We…
Compute the number of invertible 2×2 matrices over Z/(2)
Solution to Abstract Algebra by Dummit & Foote 3rd edition Chapter 1.4 Exercise 1.4.1 Prove that $|GL_2(\mathbb{F}_2)| = 6$. Solution: $GL_2(\mathbb{F}_2$ consists of precisely those $2 \times 2$ matrices over…
Compute the center of a Heisenberg group
Solution to Abstract Algebra by Dummit & Foote 3rd edition Chapter 2.2 Exercise 2.2.14 Let $F$ be a field and let $H(F)$ denote the Heisenberg group over $F$ as defined…
Exhibit an action of Sym(4) on a set of polynomials
Solution to Abstract Algebra by Dummit & Foote 3rd edition Chapter 2.2 Exercise 2.2.13 Let $n$ be a positive integer and let $R$ be the set of all polynomials with…
Sym(4) acts on a set of polynomials by permuting the variables
Solution to Abstract Algebra by Dummit & Foote 3rd edition Chapter 2.2 Exercise 2.2.12 Let $R$ be the set of all polynomials with integers coefficients in the independent variables $x_1,…
Every normalizer contains the group center
Solution to Abstract Algebra by Dummit & Foote 3rd edition Chapter 2.2 Exercise 2.2.11 Let $G$ be a group. Prove that $Z(G) \leq N_G(A)$ for any subset $A \subseteq G$.…
Normal subgroups of order 2 are central
Solution to Abstract Algebra by Dummit & Foote 3rd edition Chapter 2.2 Exercise 2.2.10 Let $H$ be a subgroup of order 2 in $G$. Show that $N_G(H) = C_G(H)$. Deduce…