MATH1071-WE01 Linear Algebra I 2019
Hello, dear friend, you can consult us at any time if you have any questions, add WeChat: daixieit
MATH1071-WE01
Linear Algebra I
2019
SECTION A
Use a separate answer book for this Section.
1. (a) Let R[x]n be the set of polynomials of degree at most n. Assume n > 1. Show
that
d
dx
is a linear map R[x]n 二 R[x]n-1 .
(b) Let n > 3 and consider the map T : R[x]n 二 R[x]n given by
T : p(x) 1二 6p(x) + p/ (x) - x2p// (x).
You may assume T is linear. Determine the nullity of T.
2. We write Mn (R) for the set of n x n matrices with real entries.
(a) Let A e Mn (R). Define
SA : Mn (R) 二 Mn (R)
by SA (B) = AB for all B e Mn (R). Show that SA is a linear map.
(b) Compute the rank and nullity of SA when
A = ╱6(3) 2(1)← .
3. (a) Determine if the following set is a basis of R4 .
,((.╱ìì 、11 ╱ìì21-2、11 ╱ìì、11 ╱ìì30-3、11、((..
((.)-2/ ) 1 / )1/ )-3/ ((.
(b) For each a e R, determine those values of X e R for which the determinant of
the following matrix is 0.
、1
ì(ì) a a a X a a a a 1(1)
ì(ì) a a X a a a a a 1(1)
ì(ì) a a a a a X a a 1(1) .
ì(ì) a a a a X a a a 1(1)
1/
4. (a) Determine if the following matrix is invertible and, if it is, compute the inverse
matrix. ╱ 1(2) ) |
2 0 1 |
2(1)、 5/ . |
(b) Give the solution set to the following system of linear equations.
w + 4x + 3y + z = 0,
w + 5x + 4y + 2z = 0,
w - x + y - z = 0.
5. We write Mn (R) for the set of n x n matrices with real entries. For A e Mn (R), we define
UA = {B e Mn (R) : AB = BA} C Mn (R)
and
VA = {B e Mn (R) : AB = -BA} C Mn (R).
You may assume that UA and VA are vector subspaces of Mn (R).
(a) In the case
A = ╱0(0) 0(0) )0 0
0(1)、
0/ ,
compute the dimensions of UA , of VA , and of UA n VA .
(b) Now let A e Mn (R). Suppose A has rank r for some r with 1 < r < n - 1. Show that UA Mn (R).
SECTION B
Use a separate answer book for this Section.
6. Find the general solution to the system of first order differential equations
x˙1 (t) = 5x1 (t) + 2x2 (t) + x3 (t) ,
x˙2 (t) = -8x1 (t) - 3x2 (t) - 2x3 (t) ,
x˙3 (t) = 4x1 (t) + 2x2 (t) + 2x3 (t) .
7. Let V be the vector space R[x]2 of real polynomials of degree at most two and let c : V 1二 V be the linear operator
c (p(x)) = λx2p// (x) + xp/ (x) + p(x + 1)
with p(x) e R[x]2 , p/ (x) = dp(x)/dx, and λ e R. Determine for which value of λ e R the linear operator c has an eigenvalue equal to 0 and in that case find the corresponding eigenfunction.
8. (a) Show that
(z, w) = 3z1 1 + iz2 1 - iz1 2 + 4z2 2
defines an inner product on V = C2 and, using this inner product, find the
norm of the vector
u = ╱ ←i(i) .
(b) Let V be the vector space R[x]2 of real polynomials of degree at most two, with
inner product
(p, q) = 10 1 p(x)q(x) dx .
Using this inner product find a basis for the orthogonal complement U一 of the vector subspace U = span{x} C V .
9. (a) Let A, B be n x n matrices such that AB = BA. If v is an eigenvector of A and if Bv 0 show that Bv is also an eigenvector for A.
(b) Let C be an n x n anti-hermitian matrix. Show that its eigenvalues are imag-
inary numbers, i.e. λ = ix with x e R.
10. Let
G = Z2 x Z3
be the direct product of the two cyclic groups Z2 and Z3 . Firstly write down the group table for G and secondly find an element of G with order 6.
2022-04-08