MATH0006 Algebra 2 exam may 2021
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MATH0006 Algebra 2 exam may 2021
1. (i) Find integers h, k such that 37h + 17k = 1. What is 17_1 in ❩3(*)7 ?
(ii) Find 17358 in ❩37 .
(iii) Solve x13 = 5 in ❩37 .
(iv) Factorise 3145 into primes in ❩ and then into primes in ❩[i], ex- plaining why they are primes. Hence find four ways of expressing 3145 in the form a2 + b2 where a, b e ◆ 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么 (n e ◆).
╱ 1 、
(iii) Let ↓么 e ❘3 be defined by ↓么+1 = A↓么 , ↓0 = 『.3(2)││. Find
lim么_oo ↓么 .
(b) (i) Let B e M么 (❘) and assume the characteristic polynomial cB (t) factorises as Π/(﹔)=1 (t - λ/ ))乞 , where the λ/ are distinct. Let e/ = dim(E入乞), where E入乞 is the eigenspace associated to λ/ . What is the condition for B to be diagonalisable?
╱ 1 a 0 、
(ii) Let B = 『.0 b c ││, where a, b, c, d e ❘. 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 AA# or otherwise, find det B .
(iv) Let C么 be the n × n matrix with entries c/λ = Σ么μ=1 k/+λ _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 ❘ and |ac| = 1}, 大 is matrix multiplication; (ii) G = {f : ❘ -→ ❘}, where (f 大 g)(x) = f(x) + g(x) for all x e ❘; (iii) G = {x e ❘ : 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 {x/yλ z μ : 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?
2022-04-20