# Test1-Version1-solutions

```MATH 2LA3 Midterm Test #1
Midterm Test
Duration of test: 50 minutes
McMaster University
February 9, 2022
Matt Valeriote
Last Name:
First Name:
Student No.:
This test has 8 pages and ten questions (some with multiple parts). The last two pages are blank
your answers when indicated to do so. For all questions, write your solutions in the space provided
for each question. Please be sure to include your student number and initials on each page of this
test.
A McMaster standard calculator (Casio fx-991 or Casio fx-991 MS) is allowed, but no other aids
are.
Marks are indicated in the margin; the maximum number of marks is 30.
Score
Question
Score
1
2
3
4
5
6
7
8
9
10
Total
MATH 2LA3 Test #1,
[5]
Student #
Initials:
Page
2
1. For each of the following statements, determine if they are true or false and circle the correct
answer (TRUE or FALSE). Each question is worth 1 mark. Do not provide justifications for
your answers. No partial credit will be given for an incorrect answer. There is no penalty for
(a) If A is an m &times; n matrix that has rank k, then A has exactly k pivot columns.
TRUE
FALSE
(b) If A is an m &times; n matrix then the non-zero rows of A form a basis for the row space of A.
TRUE
FALSE
(c) If m ≥ 1 and S = {⃗v1 , ⃗v2 , . . . , ⃗vm } is a set of non-zero vectors from Rn , then some subset
of S is a basis for the subspace Span S.
TRUE
FALSE
(d) If ⃗x is an extreme point of the set F of all feasible solutions of a canonical linear programming problem, then ⃗x is an optimal solution of the problem.
TRUE
FALSE
(e) If a canonical linear programming problem does not have an optimal solution, then either
the objective function is not bounded on the set of feasible solutions F, or F is empty.
TRUE
FALSE
MATH 2LA3 Test #1,
Student #
Initials:
Page
3
2. Consider the 4 &times; 5 matrix


1
3 −2 1
3
 5 15 1 −28 8 

A=
 4 12 −1 −17 8 
−2 −6 1
7 −6
A can be row-reduced to the matrix

1
0
B=
0
0
[2]

3 −2 1
3
0 1 −3 0 

0 0
0 −4
0 0
0
0
(you do not need to show this).
In the space below, write down the reduced row echelon form of A (so write down the matrix
rref(A)).
3. Using the matrix A from Question #2, determine the rank of A and the nullity of A. Write
[2]
(a) The rank of A =
(b) The nullity of A =
.
.
4. Using the matrix A from Question #2,
[4]
(a) find a basis for the column space of A that consists of column vectors of A. List the
vectors from this basis in the space below.
MATH 2LA3 Test #1,
Student #
Initials:
Page
4
(b) Find a basis for the null space of A and list the vectors of this basis in the space below.
5. Consider the following vectors from R3 :
 
 
 
 
1
0
6
4
⃗v1 = −3 , ⃗v2 = 1 , ⃗v3 = −6 , and p⃗ = −1 .
0
2
24
22
[3]
Show that the vector p⃗ is in Span{⃗v1 , ⃗v2 , ⃗v3 } by finding scalars a, b, c with p⃗ = a⃗v1 + b⃗v2 + c⃗v3 .
a=
,b=
,c=
.
You do not need to provide all possible values for a, b, and c.
6. Consider the following 3 &times; 3 matrix


1 1 1
C = 1 2 2 .
1 2 3
[2]
Is the matrix C invertible? Place your answer (YES or NO) in the space below. To receive
7. Consider the following canonical linear programming problem:
Maximize the objective function f (x, y) = x + 5y subject to the constraints
−x + y ≤ 11
x + y ≤ 27
2x + 5y ≤ 90
[3]
and x ≥ 0, y ≥ 0.
The extreme points of the set of feasible solutions of this problem are: A = (0, 0), B = (0, 11),
C = (5, 16), D = (15, 12), and E = (27, 0) (you do not need to show this). Answer the
following two questions:
MATH 2LA3 Test #1,
Student #
Initials:
Page
5
(a) The optimal solution of this problem is (x, y) =
provide a brief justification for your solution.
(b) The maximum value of the objective function f (x, y) at the optimal solution is
8. Consider the following simplex tableau:
x1 x2 x3 x4 x5 x6 M
0 2
4 1 0 2
0
 1 2
1 0 0 −3 0

 0 1
6 0 1 4
0
0 −2 −1 0 0 5
1


6
8 

7 
48
[3]
(a) Write down the basic feasible solution associated with this simplex tableau.
x1 =
,
x2 =
,
x3 =
,
x4 =
,
x5 =
,
x6 =
.
(b) For this basic feasible solution, what is the value of the objective function of the problem?
The value is
.
9. For this question, use the simplex tableau from the previous question.
[3]
(a) Identify the entry in the tableau to pivot on in the next step of the simplex method.
Provide the row number and column number of this entry:
Row number =
, Column number =
.
(b) Write down the simplex tableau that is produced by pivoting on this entry of the given
simplex tableau.
.
MATH 2LA3 Test #1,
Student #
Initials:
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6
10. Consider the following canonical linear programming problem:
[3]
Maximize the objective function f (x1 , x2 ) = 8x1 + 7x2 subject to the constraints
x1 + x2 ≤ 17
x1 + 2x2 ≤ 32
5x1 − 12x2 ≤ 10
and x1 ≥ 0, x2 ≥ 0.
In the space below, write down the initial simplex tableau for this problem. Note that you do
not need to solve this problem, just write down its initial simplex tableau.
1111111111111111111111111111
MATH 2LA3 Test #1,
Student #