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MATH1002
Linear Algebra
This examination has two sections: Multiple Choice and Extended Answer.
The Multiple Choice Section is worth 50% of the total examination;
there are 20 questions; the questions are of equal value;
all questions may be attempted.
Answers to the Multiple Choice questions must be entered on
the Multiple Choice Answer Sheet.
The Extended Answer Section is worth 50% of the total examination;
there are 3 questions; the questions are of equal value;
all questions may be attempted;
working must be shown.
University approved calculators may be used.
THE QUESTION PAPER MUST NOT BE REMOVED FROM THE
EXAMINATION ROOM.
Marker’s use
only
Page 1 of 22
CC1451A Semester 1, 2016 Page 2 of 22
Multiple Choice Section
In each question, choose at most one option.
Your answers must be entered on the Multiple Choice Answer Sheet.
1. The cosine of the angle between the vectors i+ 2j+ 2k and 3i+ 4k is equal to
(a)
14
225
(b)
11
15
(c)
11√
15
(d)
15
11
(e)
225
11
2. The length of the vector 3 (i− j− k) is equal to
(a) 9 (b)
√
18 (c)
√
27 (d) 18 (e)
√
3
3. If u = −i+ 2j+ 2k and v = 3i− 2j+ k then u · v is equal to
(a) 6i+ 7j− 4k (b) −5 (c) 6i− 7j+ 4k
(d) 9 (e) −9
4. The unit vector in the direction of 2i− j− 2k is
(a)
1
6
(2i− j− 2k) (b) i+ j+ k (c) i− j− k
(d)
1
5
(2i− j− 2k) (e) 1
3
(2i− j− 2k)
5. If a = −i+ j+ k and b = i− j+ k then a× b is equal to
(a) 0 (b) −2i− 2j (c) 0
(d) 2i+ 2j (e) i− j− 2k
CC1451A Semester 1, 2016 Page 3 of 22
This blank page may be used for rough working; it will not be marked. Be
sure to enter your answers on the Multiple Choice Answer Sheet.
CC1451A Semester 1, 2016 Page 4 of 22
6. The system of equations
2x − 2y − 2z = 4
x − 5z = 0
5x − 4y − 9z = 8
has the general solution
(a) x = 5, y = 2, z = 1.
(b) x = 0, y = −1, z = 0.
(c) x = 1 + 2t, y = 2 + 9t, z = t where t ∈ R.
(d) x = 5t, y = 4t + 2, z = t where t ∈ R.
(e) x = 5t, y = 4t− 2, z = t where t ∈ R.
7. Let A = P D1 P
−1, and B = P D2 P−1 where D1 =
[
1 0
0 2
]
, D2 =
[
3 0
0 1
]
, and
P =
[
1 1
1 0
]
. Then (AB)5 is
(a)
[
25 35 − 25
0 35
]
. (b)
[ −35 25 − 35
0 −25
]
. (c)
[
35 0
0 25
]
.
(d)
[
25 1
0 35
]
. (e)
[ −25 −35 + 25
0 −35
]
.
8. The determinant of the matrix
2 2 03 −1 2
1 2 −1
is equal to
(a) −4 (b) 16 (c) 4 (d) −16 (e) 0
9. Which one of the following matrices is in reduced row echelon form?
(a)
1 0 00 0 0
0 0 1
(b)
1 −3 0 −10 6 1 4
0 0 0 2
(c) [ 0 0 1 2
1 1 0 1
]
(d)
[
1 3 2
0 1 0
]
(e) None of the above.
CC1451A Semester 1, 2016 Page 5 of 22
This blank page may be used for rough working; it will not be marked. Be
sure to enter your answers on the Multiple Choice Answer Sheet.
CC1451A Semester 1, 2016 Page 6 of 22
10. Let B be a 4× 4 matrix and suppose that det(B) = 2 . Then det
(
− 1√
2
B
)
is
(a) 1/2 (b) −1/
√
2 (c) −1 (d) −
√
2 (e) −2
11. The line through the point (−1, 2, 3) perpendicular to the plane x + 2y + 7z = 0
is given by
(a) r = 4j+ 10k+ s(i+ 2j+ 7k), s ∈ R.
(b) r = −i+ 2j+ 3k+ s(i− 2j+ 7k), s ∈ R.
(c) x + 1 =
y − 2
−2 =
z − 3
7
.
(d) x− 1 = y − 2
2
=
z − 3
7
.
(e) None of the above.
12. Which one of the following implications may be false for some square matrices A, B?
(a) ABA = BAB =⇒ (AB)3 = (BA)3
(b) (A−B)2 = A2 − 2AB + B2 =⇒ AB = BA
(c) AB = BA =⇒ (A + B)(A−B) = A2 −B2
(d) det(A) = 0 =⇒ det(AB) = 0
(e) (AB)2 = 0 =⇒ AB = 0
13. If A, B and C are 3× 3 invertible matrices, and ABC =
2 0 00 2 0
0 0 2
, then the inverse
of B is
(a) 2C−1A−1. (b)
1
8
AC. (c)
1
2
A−1C−1. (d)
1
2
C−1A−1. (e)
1
2
CA.
14. Which one of the following statements is false, given that A is a matrix of size 3× 3,
B is a matrix of size 3× 2, and C is a matrix of size 2× 3?
(a) A2 + BC is a 3× 3 matrix. (b) ACB is defined.
(c) 2A + CB is not defined. (d) (BC)2 is a 3× 3 matrix.
(e) B(A−BC) is not defined.
CC1451A Semester 1, 2016 Page 7 of 22
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sure to enter your answers on the Multiple Choice Answer Sheet.
CC1451A Semester 1, 2016 Page 8 of 22
15. Consider the three planes with equations
P1 : x + 2y − z = 1,
P2 : −2x − 4y + 2z = 2,
P3 : −3x − 6y + 3z = 6.
Which of the following is true?
(a) None of the planes are parallel to each other.
(b) P1 and P2 are parallel to each other but not parallel to P3.
(c) P1 and P3 are parallel to each other but not parallel to P2.
(d) P2 and P3 are parallel to each other but not parallel to P1.
(e) All of the planes are parallel to each other.
16. Consider the following system of equations:
x + y + z − w = 0
−y + 2z − w = 0
2x + 6z − 4w = 0
Which one of the following statements about this system is true?
(a) There is a unique solution.
(b) The general solution is expressed using 1 parameter.
(c) The general solution is expressed using 2 parameters.
(d) The general solution is expressed using 3 or more parameters.
(e) There is no solution.
17. Which one of the following sequences of row operations, when applied to the matrix[
a b c
d e f
]
, produces the matrix
[
d− a e− b f − c
3a 3b 3c
]
?
(a) First R1 := R1 −R2, then R2 := 3R2, then R1 ↔ R2.
(b) First R1 ↔ R2 then R1 := 3R1, then R1 := R1 −R2.
(c) First R2 := R2 −R1, then R1 ↔ R2, then R1 := 3R1.
(d) First R1 := 3R1, then R1 ↔ R2, then R1 := R1 −R2.
(e) First R1 ↔ R2, then R1 := R1 −R2, then R2 := 3R2.
CC1451A Semester 1, 2016 Page 9 of 22
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sure to enter your answers on the Multiple Choice Answer Sheet.
CC1451A Semester 1, 2016 Page 10 of 22
18. Suppose v and w are two non-zero vectors lying in this page:
v w
Which of the following is true?
(a) (v ×w) · v is a non-zero scalar.
(b) v and v ×w are parallel.
(c) (v ×w)× v is perpendicular to both v and w.
(d) (w × v)× (v ×w) is parallel to v but not w.
(e) v ×w points upwards, towards the ceiling.
19. The two lines given by the respective parametric scalar equations
x = 3 + t
y = −5 + 2t
z = −5 − t
t ∈ R and x = −3 − 2sy = −2 − s
z = 1 + 2s
s ∈ R
(a) do not intersect. (b) intersect at the point (7, 3,−9).
(c) intersect at the point (−2,−15, 0). (d) intersect at the point (−3,−2, 1).
(e) coincide.
20. Which one of the following statements about the matrix
[ −1 1
1 −1
]
is true?
(a) −2 is an eigenvalue with eigenspace
{[
t
−t
] ∣∣∣ t ∈ R}.
(b) 0 is an eigenvalue with eigenspace
{[
t
2t
] ∣∣∣ t ∈ R}.
(c) 0 is an eigenvalue with eigenspace
{[−t
t
] ∣∣∣ t ∈ R}.
(d) 1 is an eigenvalue with eigenspace
{[−t
−t
] ∣∣∣ t ∈ R}.
(e) 2 is an eigenvalue with eigenspace
{[−t
t
] ∣∣∣ t ∈ R}.
CC1451A Semester 1, 2016 Page 11 of 22
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sure to enter your answers on the Multiple Choice Answer Sheet.
CC1451A Semester 1, 2016 Page 12 of 22
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sure to enter your answers on the Multiple Choice Answer Sheet.
CC1451A Semester 1, 2016 Page 13 of 22
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End of Multiple Choice Section
Make sure that your answers are entered on the Multiple Choice Answer Sheet
The Extended Answer Section begins on the next page
CC1451A Semester 1, 2016 Page 14 of 22
Extended Answer Section
There are three questions in this section, each with a number of parts. Write your answers
in the space provided. If you need more space there are extra pages at the end of the
examination paper.
1. (a) What is the Cartesian equation of the plane through the points P (1, 0, 0), Q(0, 2, 0)
and R(0, 0, 3)?
(b) Let L1 be the line given by the Cartesian equations
x− 1
2
=
y
−3 =
z − 2
1
.
Find the closest point R on the line L1 to the point P (1, 2, 1).
CC1451A Semester 1, 2016 Page 15 of 22
(c) Let L be the line given by the parametric vector equation
r = r0 + tv,
where r0 = i + 2j + 3k and v = −i + j − k, and let P be the plane given by the
vector equation
(r− r1) · n = 0,
where r1 = 3j+ 3k and n = i+ 3j+ k. Find the point where L and P intersect.
This is the end of Question 1.
CC1451A Semester 1, 2016 Page 16 of 22
2. (a) Find the value(s) of the parameter a for which the following system of linear equa-
tions has a unique solution.
x + ay + z = 2
x + y + az = 1
x + y + z = 1
(b) Let M =
0 1 10 1 0
−1 −1 0
. Find M−1.
CC1451A Semester 1, 2016 Page 17 of 22
(c) Let P (x) denote a polynomial function of the form P (x) = Ax2 + Bx + C, where
A,B,C are real constants. Show that for any real numbers b1, b2, b3, there is a
unique choice of A,B,C such that the following equations all hold:
P (1) = b1,
P (2) = b2,
P (3) = b3.
This is the end of Question 2.
CC1451A Semester 1, 2016 Page 18 of 22
3. (a) Let M =
0 1 00 −1 0
0 2 1
. Find the eigenvalues of M .
(b) With M as in the previous part, find an invertible matrix P such that P−1MP is a
diagonal matrix. You do not need to find P−1.
CC1451A Semester 1, 2016 Page 19 of 22
(c) Suppose that A is a 3×3 matrix which has eigenvalues −t, 0 and t for some positive
real number t. Prove that A3 is a scalar multiple of A.
This is the end of Question 3.
CC1451A Semester 1, 2016 Page 20 of 22
There are no more questions.
More space is available on the next page.
CC1451A Semester 1, 2016 Page 21 of 22
This blank page may be used if you need more space for your answers.
CC1451A Semester 1, 2016 Page 22 of 22
This blank page may be used if you need more space for your answers.
End of Extended Answer Section
This is the last page of the question paper.