MATH2022: Linear and Abstract Algebra
Creation date:2024-05-23 14:40:17
Linear and Abstract Algebra
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Assignment
MATH2022: Linear and Abstract Algebra
Lecturer: Alexander Sherman and Pieter Roffelsen
This assignment contains four questions and is worth 5% of your total
mark.
Please include your SID but not your name, as anonymous marking will be
implemented.
1. Consider the following four matrices with entries from Z2,
O =
[
0 0
0 0
]
, I =
[
1 0
0 1
]
, A =
[
0 1
0 0
]
, B =
[
1 1
0 1
]
.
Consider the set of matrices,
H = {O, I,A,B},
equipped with matrix addition and multiplication.
(a) Complete the following addition and multiplication tables for H.
+ O I A B
O
I
A
B
× O I A B
O
I
A
B
(b) Is H a field? Explain your answer.
2. Consider the following matrix with entries in Z7,
M =
1 0 23 2 1
1 2 4
.
(a) Is the matrix M invertible? Explain your answer.
(b) Determine how many solutions the following linear system has over Z7,
x+ 2z = 2,
3x+ 2y + z = 0,
x+ 2y + 4z = 3.
3. For each of the following statements, indicate whether they are true or false. If a statement
is true, prove it. If a statement is false, give a counterexample.
(a) For any two square matrices A and B of the same size, with entries from any field
F , if AB = 0, then BA = 0.
(b) For all α, β ∈ Sym(n), if α is even, then the conjugate of α by β, given by β−1αβ,
is also even.
(c) For any square matrix M , with entries from {0, 1}, if M is invertible working over
R, then M is invertible working over Z2.
4. Let G be a group with n elements and identity element e. Let α be any element of G.
Show that there must exist a natural number m, with 1 ≤ m ≤ n, such that αm = e.
Hint: consider the set
S = {α, α2, α3, . . . , αn+1} = {αm : 1 ≤ m ≤ n+ 1},
which is a subset of G.