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VCE 11 General 2023

6.09 Simultaneous equations with matrices

Worksheet
Matrix equations
1

Find the matrix that satisfies the following equations.

a

\begin{bmatrix} 6 & 1 \\ 5 & 9 \end{bmatrix} \times \begin{bmatrix} ⬚ & ⬚ \\ ⬚ & ⬚ \end{bmatrix} = \begin{bmatrix} 6 & 1 \\ 5 & 9 \end{bmatrix}

b

\begin{bmatrix} 1 & 9 \\ 9 & 2 \end{bmatrix} \times \begin{bmatrix} 1 & 0 \\ 0 & 1 \end{bmatrix} = \begin{bmatrix} ⬚ & ⬚ \\ ⬚ & ⬚ \end{bmatrix}

c

\begin{bmatrix} 3 & 2 & 8 \\ 6 & 7 & 3 \\ 4 & 3 & 8 \end{bmatrix} \times \begin{bmatrix} ⬚ & ⬚ & ⬚ \\ ⬚ & ⬚ & ⬚ \\ ⬚ & ⬚ & ⬚ \end{bmatrix} = \begin{bmatrix} 3 & 2 & 8 \\ 6 & 7 & 3 \\ 4 & 3 & 8 \end{bmatrix}

d

\begin{bmatrix} 2 & 5 & 1 \\ 3 & 2 & 7 \\ 7 & 5 & 3 \end{bmatrix} \times \begin{bmatrix} 1 & 0 & 0 \\ 0 & 1 & 0 \\ 0 & 0 & 1 \end{bmatrix} = \begin{bmatrix} ⬚ & ⬚ & ⬚ \\ ⬚ & ⬚ & ⬚ \\ ⬚ & ⬚ & ⬚ \end{bmatrix}

e

\begin{bmatrix} 5 & 5 & 3 \\ 6 & 1 & 8 \\ 8 & 2 & 3 \end{bmatrix} + \begin{bmatrix} ⬚ & ⬚ & ⬚ \\ ⬚ & ⬚ & ⬚ \\ ⬚ & ⬚ & ⬚ \end{bmatrix} = \begin{bmatrix} 5 & 5 & 3 \\ 6 & 1 & 8 \\ 8 & 2 & 3 \end{bmatrix}

2

Let A,B and C be matrices. Using matrix algebra, solve for matrix B in the following equations:

a
A B = C
b
B A = C
c
A B + C = 0
d
B A - C = 0
e
A B + C B = D
3

Let A = \begin{bmatrix} \dfrac {9}{2} & -\dfrac {5}{2} \\ \\9 & -\dfrac {9}{4}\end{bmatrix} and B=\begin{bmatrix} -2 & -1 \\ -\dfrac {7}{4} & -\dfrac {1}{3} \end{bmatrix}.

a

Find A^{ - 1 }.

b

Find X, if AX=B.

4

Find the matrix X for the given matrices and equations:

a

P = \begin{bmatrix} 13 & 3 \\ 7 & 11\end{bmatrix}, PX = P

b

N = \begin{bmatrix} 2 & -9 \\ -1 & -4\end{bmatrix} and I=\begin{bmatrix} 1 & 0 \\ 0 & 1\end{bmatrix}, X N = I

c

M = \begin{bmatrix} 1 & -5 \\ -5 & 6\end{bmatrix} and N=\begin{bmatrix} 7 & 8 \\ 9 & 1\end{bmatrix}, XM = N

d

M = \begin{bmatrix} 10 & -1 \\ -9 & 4\end{bmatrix} and N=\begin{bmatrix} 7 & -6 \\ 5 & -9\end{bmatrix}, M X = N

e

M = \begin{bmatrix} -6 & 10 \\ -6 & -4\end{bmatrix} and P=\begin{bmatrix} -6 & -10 \\ 4 & 1\end{bmatrix}, X P = M

f

M = \begin{bmatrix} 16 & -10 \\ 16 & 2\end{bmatrix} and N=\begin{bmatrix} -6 & -12 \\ -18 & -3\end{bmatrix}, M X = N

g

A = \begin{bmatrix} 10 & 3 \\8 & 4\end{bmatrix} and P=\begin{bmatrix} 5 \\ 6 \end{bmatrix}, A X = P

h

B = \begin{bmatrix} -2 & -3 \\ 3 & -10 \end{bmatrix} and Q=\begin{bmatrix} 5 \\ 6 \end{bmatrix}, B X = Q

i

A = \begin{bmatrix} -8 & 5 & 7 \\ 5 & 6 & -8 \\ 7 & 2 & 7 \end{bmatrix} and B=\begin{bmatrix} -10 \\ 1 \\ -8 \end{bmatrix}, A X = B

j

M = \begin{bmatrix} -2 & -8 \\ -1 & -6.6\end{bmatrix} and N=\begin{bmatrix} 5.4 & 1.7 \\ 4 & -3\end{bmatrix}, M X = N

k

M = \begin{bmatrix} -3 & -5 \\ 3 & 0\end{bmatrix}, N=\begin{bmatrix} 5 & 2 \\ 0 & -2 \end{bmatrix} and P=\begin{bmatrix} 6 & 10 \\ 10 & -9 \end{bmatrix}, MNX = P

l

M = \begin{bmatrix} 3 & 1 \\ -4 & 5\end{bmatrix}, N=\begin{bmatrix} 2 & -3 \\ 3 & -5 \end{bmatrix} and P=\begin{bmatrix} -6 & 10 \\ 5 & 5 \end{bmatrix}, M^{ - 1 } N X = P

Simultaneous equations
5

The following matrix equations represent systems of linear equations:

i

Write the system of two linear equations represented by the matrix.

ii
Solve the system of equations using an algebraic method.
a
\begin{bmatrix} x + y \\ x - y\end{bmatrix} = \begin{bmatrix} 5 \\ 7 \end{bmatrix}
b
\begin{bmatrix} x - y \\ 4x + y \end{bmatrix} = \begin{bmatrix} 5 \\ -4 \end{bmatrix}
6

Given the following systems of linear equations:

i

Express the system of equations in matrix form.

ii

Find the determinant of the coefficient matrix.

iii

Solve the system of equations using matrices.

a

\begin{aligned} x + 3 y &= 23 \\ 4 x + 2 y &= 32 \end{aligned}

b

\begin{aligned} 4x + y &= 49 \\ 4 x + 5 y &= 101 \end{aligned}

c

\begin{aligned} 12x + 16 y &= 32 \\ 3 x + 28 y &= 20 \end{aligned}

d

\begin{aligned} 3x + 4 y &= 24.9 \\ 6 x + 7 y &= 45.9 \end{aligned}

e

\begin{aligned} 5x + y &= 13.33 \\ 2 x + 4 y &= 9.4 \end{aligned}

f
\begin{aligned} x + y &= 1 \\ x + 3 y &= 5 \end{aligned}
7

Given the following system of linear equations:

\begin{aligned} 4 x + 6 y &= 23 \\ 8 x + 12 y &= 61 \end{aligned}

a

Express the system of equations in matrix form.

b

Calculate the determinant of the coefficient matrix.

c

Explain what the value of the determinant indicates.

8

For each of the following systems of linear equations:

i

Express the system of equations in matrix form.

ii

Calculate the determinant of the coefficient matrix.

iii

Sketch the lines described by the two equations on the same axes.

iv

Comment on the number of solutions to the system of equations.

a

\begin{aligned} -2 x + 3 y &= 2 \\ -8 x + 12 y &= 8 \end{aligned}

b

\begin{aligned} \dfrac{x}{4} - y &= - 2 \\ \dfrac{x}{2} - 2 y &= 0 \end{aligned}

9

Given the following system of linear equations:

3 y = - 6 x + 42

4 y = - 2 x + 20

a

Express the system of equations in matrix form.

b

Calculate the determinant of the coefficient matrix.

c

Solve the system of equations using matrices.

10

Consider the lines 4 x + 2 y = 8 and 5 x + 5 y = 25:

a

Express the system of equations in matrix form.

b

If A is the coefficient matrix in part (a), find A^{ - 1 }.

c

Solve the system of equations using matrices.

11

x and y are two numbers, where x > y. The sum of the numbers is 42, and the difference is 16.

a

Write two equations that describe the relationship between x and y in the form \\a x + b y = c.

b

Express the system of equations in matrix form.

c

Calculate the determinant of the coefficient matrix.

d

Solve the system of equations using matrices.

12

Given the following system of linear equations:

\begin{aligned} 2 x + 4 y + 5 z &= 45\\ 5 x + y + z &= 37 \\ x + 3 y + 6 z &= 42 \end{aligned}

a

Express the system of equations in matrix form.

b

Solve the system of equations using matrix inverse methods and your CAS calculator.

Applications
13

A farmer has two paddocks, one with area x \text{ m}^2, and another with area y \text{ m}^2. The total area of both paddocks is 2600 \text{ m}^2 . The farmer has planted \dfrac{x}{2} \text{ m}^2 and \dfrac{2 y}{3} \text{ m}^2 in corn and this adds up to 1600 \text{ m}^2 of corn.

a

Write two equations in terms of x and y in the form a x + b y = c.

b

Express the system of equations in matrix form.

c

Evaluate the determinant of the coefficient matrix.

d

Solve the system of equations using matrices.

14

At a school canteen, students can order the Healthy snack which contains 4 pieces of fruit and 2 savoury snacks, or they can order the Yummy snack which contains 1 piece of fruit and 3 savoury snacks.

On a given day the canteen used 260 pieces of fruit and 140 savoury snacks.

a

Let h represent the number of Healthy snacks and y represent the number of Yummy snacks.

i

Construct an equation for the total amount of fruit used.

ii

Construct an equation for the total savoury snacks used.

b

Express the system of equations in matrix form.

c

Use your CAS calculator and matrix inverse methods to determine the number of Healthy snacks and Yummy snacks made that day.

15

An investment fund offers two types of investments, the Blue Chip and the Strong Growth. The Blue Chip requires the purchase of 250 mining company shares and 80 speculative shares. The Strong Growth requires the purchase of 150 mining company shares and 600 speculative shares. The cost of investment in the Blue Chip is \$13\,170 and the cost of investment in the Strong Growth is \$21\,150.

a

Let m represent the cost of mining company shares and s represent the cost of speculative shares.

i

Construct an equation for the total cost of the Blue Chip investment.

ii

Construct an equation for the total cost of the Strong Growth investment.

b

Express the system of equations in matrix form.

c

Use your CAS calculator and matrix inverse methods to determine the cost of the mining company shares and the cost of the speculative shares.

16

A company determines that they spend a total of 63 hours per week on various forms of advertising media. The amount of time spent on print media is 3 hours more than social and video media combined. 2 hours more is spent on video media than social media.

a

Let s, v and p represent the hours spent on social, video and print media respectively. Construct a set of linear equations to represent this information.

b

Express the system of equations in matrix form.

c

Use your CAS calculator and matrix inverse methods to determine the number of hours each week spent on the three forms of advertising.

17

The angles in a triangle are such that the larger angle, z, is double the smaller angle, x. The third angle, y, is 30 \degree less than the larger angle, z.

a

Construct a system of three linear equations to represent this information.

b

Express the system of equations in matrix form.

c

Use your CAS calculator and matrix inverse methods to determine the angles of the triangle.

18

A quadratic function in the form y =a x^{2}+ bx +c contains the points A \left( - 1 , 5\right),\\ B \left(0, 10\right) \text{ and C} \left(4, - 10 \right).

a

Substitute the given points into y =a x^{2}+ bx +c to form three equations in terms of a, b, and c.

b

Express the system of equations in matrix form.

c

Use your CAS calculator and matrix inverse methods to determine the values of the coefficients a, b \text{ and } c.

19

A study determined that for the city of Fairview there is a relationship between the following three variables:

  • The annual window tinting revenue R (in thousands of dollars)
  • The number of cars registered C (in millions)
  • The annual amount spent on car insurance I (in thousands of dollars)
The relationship found in the study is given by:R = a + b C + c I Where a, b and c are constants. The given table shows the figures for the three variables in 2017, 2018 and 2019.
a

Use the relationship found in the study to construct a system of three linear equations to represent the information given in the table.

b

Express the system of equations in matrix form.

c

Use your CAS calculator and matrix inverse methods to determine the values of the coefficients a, b, c. Round each coefficient to two decimal places.

RCI
201710\,150113.5890
201815\,4321421210
201922\,450162.71494
20

Three different smart phone models, the Galactic 6S, 6V and 6P are produced at three different factories. The table given represents the number produced in each factory in November 2019. The total costs are \$136\,400, \$137\,200 and \$186\,600 for factory A, B and C respectively.

Use your CAS calculator and matrix inverse methods to determine the cost of making each model.

6S6V6P
Factory A10001200800
Factory B8009001000
Factory C120015001200
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Outcomes

U1.AoS3.4

determinant and inverse of a matrix

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