MATH1071-WE01 Linear Algebra I 2020
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MATH1071-WE01
Linear Algebra I
2020
SECTION A
Q1 1.1 Let Π be the plane in 皿3 passing through the points
╱ 3(3) 、 ╱ 、3(1) ╱ 1(2) 、
(i) Find the equation of Π in the form ax + by + cz = d.
(ii) If L is the line in 皿3 passing through both the origin and the point ╱ 、,
at what point in 皿3 does L intersect Π?
1.2 Calculate the area of the parallelogram in 皿2 with the following vertices: ╱ 、1(1) , ╱ 、2(2) , ╱ 、2(4) , and ╱ 、3(5) .
Q2 2.1 Find the inverse of the following matrix, clearly outlining your method.
╱ 、
.)1 0 0 2 .
2.2 Determine the value of t à 皿 for which the linear system of equations
x1 + 2x2 + 3x3 = t,
2x1 + 2x2 + 2x3 = 1,
3x1 + 2x2 + x3 = 1,
has a solution. Find the general solution in this case.
Q3 Let Mn (皿) be the real vector space consisting of all n ( n matrices with real entries.
3.1 Suppose A1 , A2 , . . . , Ak are k linearly independent matrices in Mn (皿), and that
P and Q are two invertible matrices in Mn (皿). Show that the k matrices PA1 Q, PA2 Q, . . . , PAk Q,
are linearly independent.
3.2 For any fixed matrix B in Mn (皿), show that the subset
WB = |A à Mn (皿) : AB = )BA女
is a vector subspace of Mn (皿).
3.3 Assume A and B are two matrices in Mn (皿) such that AB = )BA. Prove that A and B cannot both be invertible if n is odd.
Q4 Consider the linear map S : 皿4 ≠ 皿4 defined by
╱ x 、 ╱ x ) z 、
S...... = ...... .
4.1 Find the matrix A representing S, with respect to the standard basis vectors of 皿4 , and determine the rank and nullity of A.
4.2 Find a basis for ker(S) and im(S) and show that
ker(S) | im(S) = |0女.
4.3 Hence, or otherwise, prove that
ker(S) è im(S) = 皿4 .
Q5 Let 皿[x]n be the (n+1)-dimensional vector space consisting of all polynomials whose
coefficients are real and whose degree is at most n.
For each k = 0, 1, . . . , n define the linear map Tk : 皿[x]n ≠ 皿[x]n by
Tk (p(x)) = p (x) + p(1)x/k ,
where we write p/ for the first derivative of p (with respect to the variable x).
5.1 Prove that ker(Tn ) = |0女, where 0 is the zero polynomial. Hence, determine the rank of Tn .
5.2 For any k < n, evaluate Tk (pk (x)), where
k + 2 xk+1
k + 1 k + 1 .
Hence, or otherwise, determine the values of k for which Tk is an isomorphism.
5.3 For the case n = 3, write down the matrix representing T2 with respect to the standard basis of 皿[x]3 .
SECTION B
Q6 Given the matrix
A = ╱、
.0 0 )2. ,
find P such that P-1 AP is diagonal, clearly outlining your method. Use this result to compute A10 (brute force calculation is not allowed).
Q7 Let V be the vector space 皿[x]3 of real polynomials of degree at most three and let
4 : V |≠ V be the linear operator
4 (p(x)) = p(x + 1) ) (0 x p(y)dy ,
with p(x) à 皿[x]3 and a à 皿. Find the matrix representing the linear operator 4 on V using the standard basis |1, x, x2 , x3 女. Show that for a = 4 one of the eigenvalues of the operator 4 is equal to )1 and then compute the eigenfunction corresponding to this eigenvalue.
Q8 8.1 Find the necessary conditions on the real parameters a and b so that (x, y) = 3x1y1 + x1y2 + ax2y1 + 2x2y2 + x3y2 + x2y3 + bx3y3
defines an inner product on V = 皿3 .
8.2 If V = 皿4 is given the standard inner product, find an orthonormal basis for the subspace determined by the equation
x1 )x2 + x3 )x4 = 0 ,
and then extend this basis to an orthonormal basis for all V = 皿4 .
Q9 Let V be a complex vector space with inner product < , > and let 4 : V ≠ V be
a linear hermitian operator with respect to this inner product. First prove that the eigenvalues of 4 must be real and then show that if z, w à V are eigenvectors of 4 corresponding to different eigenvalues then they must be orthogonal.
Q10 Let H be the set of matrices of the form
A = ╱0(1) 1(a) .0 0
b(c)、
1. ,
with a, b, c à 勿. Show that H is a group with respect to matrix multiplication. Is the group abelian? Justify your answer. [You may assume associativity]
2022-04-08