MATH0006 2021
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MATH0006
1. (i) Find integers h, k such that 37h + 17k = 1. What is 17_1 in Z3(*)7 ?
(ii) Find 17358 in Z37 .
(iii) Solve x13 = 5 in Z37 .
(iv) Factorise 3145 into primes in Z and then into primes in Z[i], ex- plaining why they are primes. Hence find four ways of expressing 3145 in the form a2 + b2 where a, b e N with a 2 b. Explain briefly why there are no other ways.
╱ 1/5
2 . (a) Let A = . 2/5
( 2/5
2/5
1/5
2/5
2/5 、
2/5 .
(i) Find an invertible matrix P and a diagonal matrix D such that P_1 AP = D .
(ii) Find an explicit formula for A脯 (n e N).
╱ 1 、
(iii) Let v脯 e R3 be defined by v脯+1 = Av脯 , v0 = .(3(2)... Find
lim脯_oo v脯 .
(b) (i) Let B e M脯 (R) and assume the characteristic polynomial cB (t) factorises as Πi(r)=1 (t - λi )fi, where the λi are distinct. Let ei = dim(E入i), where E入i is the eigenspace associated to λi . What is the condition for B to be diagonalisable?
╱ 1 a 0 、
(ii) Let B = .( 0 b c.., where a, b, c, d e R. Find for which values of
a, b, c and d the matrix B is diagonalisable, explaining your reasoning.
╱ 1 3. (i) Find det -21 ( 2 ╱ 1 (ii) Let A = a2(a) ( a3 |
2 0 1 3 1 b b2 b3 |
1 0 、 ., showing the steps in your calculation. 5 4 . 1 1 、 c2 d2 .(.) c3 d3 . |
Find an expression for det A as a product of linear factors, explaining your answer.
(iii) Let B be the matrix
╱ 4 a + b + c + d a2 + b2 + c2 + d2 a3 + b3 + c3 + d3 、
. .
( a3 + b3 + c3 + d3 a4 + b4 + c4 + d4 a5 + b5 + c5 + d5 a6 + b6 + c6 + d6 . By considering AAT or otherwise, find det B .
(iv) Let C脯 be the n × n matrix with entries cij = Σk(脯)=1 ki+j _2 . What is det C5 ? (You may leave your answer in terms of factorials.)
4. (a) Determine if each of the following sets G under operation 大 forms a group, justifying your answer:
(i) G = {│ 0(a) c(b) 、 : a, b, c e R and |ac| = 1}, 大 is matrix multiplication; (ii) G = {f : R -→ R}, where (f 大 g)(x) = f(x) + g(x) for all x e R; (iii) G = {x e R : x 2 0}, a 大 b = |b - a|.
(b) Let G be the group with presentation
(x, y, z : x3 = y2 = z2 = e, yx = xz, zx = xyz, yz = zy)
and normal form {xiyj zk : 0 < i < 2, 0 < j < 1, 0 < k < 1}.
(i) Find the order of each element of G.
(ii) The non-trivial groups of order < 6 are C2 , C3 , C4 , C2 × C2 , C5 , C6 , S3 . For each of these groups, how many subgroups of G are there isomorphic to it?
2022-07-29