MATH0006 Section A
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MATH0006
Section A
1.
(a) (i) Find integers h, k such that 29h + 11k = 1. What is 1¯1- 1 in Z2(*)9 ?
2798
(iii) Solve x25 = 2 in Z29 .
(b) Let S = Z[^−2] = {a + b^−2 : a, b ∈ Z}. What does it mean to say that S has
2. ╱ 1(1) (a) Find det .(.) 2 ( |
2 3 5 1 |
、││, showing the steps in your calculation. 2 1 . |
(b) Let A = .(、) . Find an invertible matrix P and a diagonal matrix
(25 marks)
Section B
3.
(a) (i) Let A, B and C be n × n matrices. Show that det ╱C(A)
B(0)、 = det A det B .
(ii) Show that det ╱A2AC(+)C2
(b) (i) Let C be the matrix ╱z(x)
.y
product of linear factors.
A(C)2(A)、 = (det A)4 .
.(、) . Use row operations to express det C as a
(ii) Let A = .(╱) .(、) . Use part (i) to find the eigenvalues of A. Deduce that
if b c then A is diagonalisable. Is A diagonalisable if b = c?
[You will need to use ω = e2亓i/3 in (b) . Recall that ω 3 = 1 and 1 + ω + ω 2 = 0]
(25 marks)
4.
(a) For each of the following sets G and operations + determine, with justification, whether or not (1) + is a closed binary operation (2) + is associative, (3) there is
an identity element, (4) all elements have an inverse, (5) G under + is a group (i) G = M2 (R), the set of 2 × 2 matrices with real entries, A+B = A + B + I2 ; (ii) G = R, a+b = a + b + a5 b5 .
(b) Let G be a group: we define the centre Z(G) of G to be the set {g ∈ G : gh = hg for all h ∈ G}. For g, h ∈ G, we define the commutator [g, h] as g- 1 h- 1gh.
(i) Show that Z(G) is a subgroup of G.
(ii) Suppose g, h ∈ G and [g, h] ∈ Z(G). Show that for positive integers n, [g) , h] = [g, h]) = [g, h) ]
(iii) Suppose g, h ∈ G and [g, h] ∈ Z(G). Show that if g and h have coprime orders, then gh = hg
(25 marks)
2022-07-29