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VCE 11 General 2023

6.04 Scalar multiplication

Worksheet
Scalar multiplication
1

\text{If }A = \begin{bmatrix} 8 & 4 \\ 12 & -10 \end{bmatrix} \text{, find:}

a
2A
b
-4A
c
\dfrac{1}{2}A
2

\text{If }A = \begin{bmatrix} -7 & 8 & 14 \\ 0 & 15 & 20 \end{bmatrix} \text{, find:}

a
3A
b
-A
c
10A
d
\dfrac{1}{2}A
3
\text{If }A = \begin{bmatrix} 8 & -3 \\ 2 & 10 \end{bmatrix} \text{and } B = \begin{bmatrix} 6 & 10 \\ -1 & 5 \end{bmatrix} \text{, find:}
a
4A + B
b
2A - B
c
5A + 3B
d
4A - 2B
e
\dfrac{1}{2}A + \dfrac{1}{4}B
4
\text{If } A = \begin{bmatrix} 2.25 & -1.5 \\ 4.5 & 8.25 \end{bmatrix} \text{and } B = \begin{bmatrix} 5.5 & 1.25 \\ -1 & 6.5 \end{bmatrix}, \text{ find:}
a
4A + 2B
b
2A - 2B
c
3A + 5B
5

\text{Let } A = \begin{bmatrix} 5 & -4 \\ 3 & 0 \end{bmatrix} \text{, } B = \begin{bmatrix} -10 & 6 \\ 2 & -1 \end{bmatrix} \text{and } C = \begin{bmatrix} 8 & 5 \\ -1 & 4 \end{bmatrix}. Find 4A - B + 2C.

Matrix equations
6

Solve for n:

a
3 \begin{bmatrix} 5 & 2 \\ -1 & 7 \end{bmatrix} + 2 \begin{bmatrix} 4 & -1 \\ n & -6 \end{bmatrix} = \begin{bmatrix} 23 & 4 \\ 17 & 9 \end{bmatrix}
b
4 \begin{bmatrix} 3 & 1 \\ -2 & n \end{bmatrix} - 3 \begin{bmatrix} 5 & 2 \\ -3 & 8 \end{bmatrix} = \begin{bmatrix} -3 & -2 \\ 1 & 40 \end{bmatrix}
c
2 \begin{bmatrix} 8 & 2 \\ -1 & 5 \\ 4 & -3 \end{bmatrix} - \begin{bmatrix} 10 & 1 \\ 6 & -2 \\ 12 & 9 \end{bmatrix} = \begin{bmatrix} 3n & 3 \\ -8 & 12 \\ -4 & -15 \end{bmatrix}
7

Solve the following matrix equations for matrix A:

a
2 \begin{bmatrix} 8 & 4 \\ -2 & 5 \end{bmatrix} + A = \begin{bmatrix} 22 & 18 \\ 10 & -8 \end{bmatrix}
b
4 \begin{bmatrix} 3 & -1 \\ 6 & 0 \end{bmatrix} - 2A = \begin{bmatrix} 14 & 8 \\ 12 & -24 \end{bmatrix}
Applications
8

The cost matrix for four products at a health store is given by the matrix:

C = \begin{bmatrix} 9.50 & 10.20 & 8.90 & 12.50 \end{bmatrix}

The store adds 120 \% to the cost price to generate the sales price.

a

Find the sales price of the four products and write them in a 1 \times 4 matrix.

b

Find the profits from each of the four products and write them in a 1 \times 4 matrix.

9

In a particular town, 30\% of households own no pets, 50\% of households own one pet, 15\% of households own two pets and 5\% of households own more than two pets.

a

Organise the percentages into a 1 \times 4 row matrix in the same order as stated above.

b

If there are 300 households in the town, multiply your matrix to find the number of households in each category. Express your answer as a 1 \times 4 matrix.

10

A pizzeria is about to mark up prices on their items by 140\%. The table shows their current prices:

Using scalar product, find the marked up prices. Express your answer as a 3 \times 2 matrix.

PizzaDrinks
Small\$6\$3
Medium\$8\$4.50
Large\$12\$6
11

Glorious Jeans will be offering a 25\% discount on all food items for their Boxing Day sales. The table shows their regular prices:

Using scalar product, find the discounted prices. Express your answer as a 3 \times 2 matrix.

SmallLarge
Sandwiches\$4.50\$7
Pies\$5\$8.50
Cakes\$6\$9.20
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Outcomes

U1.AoS3.3

matrix arithmetic: the definition of addition, subtraction, multiplication by a scalar, multiplication, the power of a square matrix, and the conditions for their use

U1.AoS3.9

add and subtract matrices, multiply a matrix by a scalar or another matrix, and raise a matrix to a power

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