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# Exam taker for Linear Algebra (Uni melb) MAST10007

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I need someone to sit my Linear Algebra exam for me tomorrow (4/11/2021) at 10:00am Melbourne time (GMT+11). Linear Algebra is a Melbourne uni subject with the subject code MAST10007. I have attached an example of what the exam will be like.

##### Additional Instructions:

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Student
number
Semester 2 Assessment, 2021
School of Mathematics and Statistics
MAST10007 Linear Algebra
Reading time: 30 minutes — Writing time: 3 hours — Upload time: 30 minutes
This exam consists of 25 pages (including this page) with 12 questions and 125 total marks
Permitted Materials
• This exam and/or an offline electronic PDF reader, one or more copies of the masked
exam template made available earlier and blank loose-leaf paper.
• One double sided A4 page of notes (handwritten only).
• No calculators are permitted. No headphones or earphones are permitted.
Instructions to Students
• Wave your hand right in front of your webcam if you wish to communicate with the
supervisor at any time (before, during or after the exam).
• You must not be out of webcam view at any time without supervisor permission.
• You must not write your answers on an iPad or other electronic device.
• Off-line PDF readers (i) must have the screen visible in Zoom; (ii) must only be used to
read exam questions (do not access other software or files); (iii) must be set in flight mode
or have both internet and Bluetooth disabled as soon as the exam paper is downloaded.
Writing
• Marks are awarded for
– Using appropriate mathematical techniques.
– Showing full working, including results used.
– Accuracy of the solution.
– Using correct mathematical notation.
• If you are writing answers on the exam or masked exam and need more space, use blank
paper. Note this in the answer box, so the marker knows.
• If you are only writing on blank A4 paper, the first page must contain only your student
number, subject code and subject name. Write on one side of each sheet only. Start each
question on a new page and include the question number at the top of each page.
Scanning and Submitting
• You must not leave Zoom supervision to scan your exam. Put the pages in number
order and the correct way up. Add any extra pages to the end. Use a scanning app to
scan all pages to PDF. Scan directly from above. Crop pages to A4.
• Submit your scanned exam as a single PDF file and carefully review the submission in
Gradescope. Scan again and resubmit if necessary. Do not leave Zoom supervision until
you have confirmed orally with the supervisor that you have received the Gradescope
confirmation email.
• You must not submit or resubmit after having left Zoom supervision.
c©University of Melbourne 2021 Page 1 of 25 pages Can be placed in Baillieu Library
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MAST10007 Linear Algebra Semester 2, 2021
Question 1 (11 marks)
Consider the linear system
x+ 2y + 3z = 6
4x+ 5y + 6z = 15
7x+ 8y + 9z = 24
(a) Reduce the augmented matrix [A|b] of the system to reduced row-echelon form. Indicate
the row operations used in each step.
(b) Determine the ranks of A and [A|b] and interpret your answer.
(c) Find the solution set of the system.
(d) Find the solution set of the corresponding homogeneous system.
(e) Prove that the set of all choices for c such that [A|c] can be solved, forms a plane through
the origin in R3.
(f) Find a normal vector to the plane in part (e).
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MAST10007 Linear Algebra Semester 2, 2021
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MAST10007 Linear Algebra Semester 2, 2021
Question 2 (8 marks)
(a) Let A be an n× n matrix. Prove that the determinant of A equals zero if and only if the
nullity of A is greater than or equal to 1.
(b) Let u ∈ R3, and consider the linear transformation T : R3 → R3 such that
T (v) = u× v.
What is the determinant of [T ]? Justify your answer.
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MAST10007 Linear Algebra Semester 2, 2021
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MAST10007 Linear Algebra Semester 2, 2021
Question 3 (14 marks)
Let L1 be the line
x− 3
−1
=
y − 8
−2
= z + 2
and let L2 be the line
x = 4− 3s, y = −1 + 5s, z = −4 + 4s, s ∈ R.
(a) Find the point of intersection of L1 and L2.
(b) Find the angle between the lines L1 and L2.
(c) Find a Cartesian equation of the plane in R3 that contains both L1 and L2.
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MAST10007 Linear Algebra Semester 2, 2021
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MAST10007 Linear Algebra Semester 2, 2021
Question 4 (9 marks)
Let V = R2 be the real vector space with vector addition ⊕ defined by
(x1, x2)⊕ (y1, y2) = (x1 + y1 − 1, x2 + y2 − 2) for each (x1, x2), (y1, y2) ∈ V
and scalar multiplication � defined by
α� (x1, x2) = (αx1 − α+ 1, αx2 − 2α+ 2) for each (x1, x2) ∈ V and α ∈ R.
(a) Verify the associative property u⊕ (v ⊕w) = (u⊕ v)⊕w when
u = (−3, 1), v = (5, 4), w = (2, 7).
(b) Prove 1� u = u for all u ∈ V .
(c) Prove the distributive property (α+β)�u = (α�u)⊕ (β�u) for all u ∈ V and α, β ∈ R.
(d) Find the zero vector 0 in V . Show that u⊕ 0 = u for all u ∈ V .
Page 8 of 25 pages
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MAST10007 Linear Algebra Semester 2, 2021
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MAST10007 Linear Algebra Semester 2, 2021
Question 5 (12 marks)
Determine if the following sets are subspaces of the real vector space M2,2 of 2× 2 matrices.
If the set is a subspace, you must use the subspace theorem to prove it. If the set is not a
subspace, then you must provide an explicit counter-example.
(a) The set S of all matrices A such that AD = DA, where D =
[
1 2
3 4
]
.
(b) The set M of all matrices of the form
[
s+ 3 s+ t
0 2t+ 6
]
where s, t ∈ R.
(c) The set W of all matrices of the form
[
r 0
0 r2
]
where r ∈ R.
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MAST10007 Linear Algebra Semester 2, 2021
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MAST10007 Linear Algebra Semester 2, 2021
Question 6 (12 marks)
Let W be the subspace of P3 spanned by
S = {1 + 2x+ 3x3, 2 + 4x+ 6x3, 1 + x2 + x3, 5 + 3x+ 5x2 + 8x3, 3− 5x+ x2 − 2x3}.
You may assume that
A =
1 2 1 5 3
2 4 0 3 −5
0 0 1 5 1
3 6 1 8 −2
∼
1 2 0 0 2
0 0 1 5 1
0 0 0 3 −9
0 0 0 0 0
= B.
(a) Is W equal to P3? Explain.
(b) Find a basis B for W consisting of polynomials in S.
(c) What is the dimension of W?
(d) For each vector in S that is not in B, find the coordinate vector with respect to the basis
B.
(e) Let C = {2 + 4x+ 6x3, 1 + x2 + x3, 3− 5x+ x2 − 2x3}.
(i) Is C linearly independent? Explain.
(ii) Is C a basis for W? Explain.
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MAST10007 Linear Algebra Semester 2, 2021
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MAST10007 Linear Algebra Semester 2, 2021
Question 7 (10 marks)
Let P2 be the vector space of real polynomials of degree ≤ 2 with ordered basis B = {1, x, x2}.
Let T : P2 → R4 be the linear transformation defined by
T (p(x)) = (p(0),p(1),p(−1),p(3)).
(a) What is T (x2 − 3x)?
(b) Find the matrix representation of T with respect to the basis B and the standard basis S
of R4.
(c) Compute the rank of T .
(d) Is T surjective? Explain your answer.
(e) Is T injective? Explain your answer.
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MAST10007 Linear Algebra Semester 2, 2021
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MAST10007 Linear Algebra Semester 2, 2021
Question 8 (9 marks)
For each of the following linear transformations, determine the
(i) image (ii) kernel (iii) inverse transformation, if it exists.
(a) Reflection R : R2 → R2 in a line ` ⊂ R2 passing through the origin.
(b) The map P : R3 → R3 given by orthogonal projection onto a plane Π through the origin
in R3.
(c) The differentiation function D : P3(R)→ P2(R) mapping a polynomial p(x) to its deriva-
tive
dp
dx
.
Hint: You do not need to find the matrix representations of the transformations.
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MAST10007 Linear Algebra Semester 2, 2021
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MAST10007 Linear Algebra Semester 2, 2021
Question 9 (14 marks)
Consider the complex matrix
A =
[
6 2 + 2i
2− 2i 4
]
.
(a) Show that A is a Hermitian matrix.
(b) Find the eigenvalues of A.
(c) Find the eigenspace corresponding to each eigenvalue of A.
(d) Find a unitary matrix U and a diagonal matrix D such that
A = UDU−1.
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MAST10007 Linear Algebra Semester 2, 2021
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MAST10007 Linear Algebra Semester 2, 2021
Question 10 (8 marks)
(a) Let A be an arbitrary 2× 2 matrix.
(i) Determine the characteristic equation of A.
(ii) Show that the characteristic equation of A can be written as
λ2 − Tr(A)λ+ det(A) = 0.
(b) Let V be a real vector space equipped with an inner product 〈u,v〉. Using the inner
product space axioms, prove that for any u,v ∈ V,
‖u + v‖2 + ‖u− v‖2 = 2‖u‖2 + 2‖v‖2.
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MAST10007 Linear Algebra Semester 2, 2021
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MAST10007 Linear Algebra Semester 2, 2021
Question 11 (9 marks)
Let u = (u1, u2) ∈ R2, v = (v1, v2) ∈ R2 and
〈u,v〉 = 3u1v1 − u1v2 − u2v1 + 6u2v2.
(a) Write 〈u,v〉 in terms of a symmetric matrix.
(b) Show that 〈u,v〉 defines an inner product on R2.
(c) Find the angle between u = (2, 1) and v = (1, 2) with respect to this inner product.
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MAST10007 Linear Algebra Semester 2, 2021
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MAST10007 Linear Algebra Semester 2, 2021
Question 12 (9 marks)
Find an orthonormal basis for P2 with respect to the inner product
〈p,q〉 =
∫ 1
−1
p(x)q(x) dx
by applying the Gram Schmidt algorithm to the basis
{v1,v2,v3} = {1, x, x2}.
Page 24 of 25 pages
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MAST10007 Linear Algebra Semester 2, 2021
End of Exam — Total Available Marks = 125
Page 25 of 25 pages

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