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VCE 11 General 2023

6.04 Scalar multiplication

Lesson

Scalar multiplication

A scalar is a quantity described by a single numerical value. Scalar multiplication is the process of multiplying a matrix by a scalar (number). Scalar multiplication can be applied to any matrix and involves multiplying each element within the matrix by the given scalar.

In general, the multiplication of a matrix by a scalar will appear similar to this: \lambda \begin{bmatrix} a&b\\ c&d \end{bmatrix}= \begin{bmatrix} \lambda a & \lambda b\\ \lambda c & \lambda d\\ \end{bmatrix}

where Lambda, \lambda, represents the scalar quantity.

Examples

Example 1

If A = \begin{bmatrix} 2 & -6 \\ -4 & 3 \end{bmatrix}, determine 3A.

Worked Solution
Create a strategy

Multiply each element of matrix A by 3.

Apply the idea
\displaystyle 3A\displaystyle =\displaystyle 3\begin{bmatrix} 2 & -6 \\ -4 & 3 \end{bmatrix}Write the equation and substitute matrix A
\displaystyle =\displaystyle \begin{bmatrix} 3\times 2 & 3\times (-6) \\ 3\times (-4) & 3\times 3 \end{bmatrix}Multiply each element by 3
\displaystyle =\displaystyle \begin{bmatrix} 6&-18\\-12&9 \end{bmatrix}Evaluate each element

Example 2

Determine \dfrac{1}{2}A+\dfrac{2}{3}B if A =\begin{bmatrix} 6&-12\\ 4&14 \end{bmatrix} and B =\begin{bmatrix} 24&3\\ -12&0 \end{bmatrix}.

Worked Solution
Create a strategy

Multiply each of the elements in matrix A by \dfrac{1}{2} and multiply each of the elements in matrix B by \dfrac{2}{3}. Add corresponding elements of the matrices \dfrac{1}{2}A and \dfrac{2}{3}B.

Apply the idea
\displaystyle \dfrac{1}{2}A+\dfrac{2}{3}B\displaystyle =\displaystyle \dfrac{1}{2}\begin{bmatrix} 6&-12\\ 4&14 \end{bmatrix}+\dfrac{2}{3}\begin{bmatrix} 24&3\\ -12&0 \end{bmatrix}Write the equation with the matrices
\displaystyle =\displaystyle \begin{bmatrix} 3&-6\\ 2&7 \end{bmatrix}+\begin{bmatrix} 16&2\\ -8&0 \end{bmatrix}Complete the scalar multiplications \dfrac{1}{2}A and \dfrac{2}{3}B
\displaystyle =\displaystyle \begin{bmatrix} 19&-4\\ -6&7 \end{bmatrix}Add each of the corresponding elements

Example 3

The cost matrix C shows the current cost, in dollars, per square metre of four different manufacturing materials.

C=\begin{bmatrix} 50& 120 & 90 & 70 \end{bmatrix}

Due to an increase in supplier prices, the cost of each material is expected to rise by 8\%. Determine the new cost matrix after the price increase.

Worked Solution
Create a strategy

Use scalar multiplication to change each element in the matrix by the same percentage.

Apply the idea

An increase of 8\% can be represented as a scalar as 1.08.

\displaystyle \text{New cost matrix}\displaystyle =\displaystyle 1.08 \times \begin{bmatrix} 50& 120 & 90 & 70 \end{bmatrix}Multiply the original cost matrix by 1.08
\displaystyle =\displaystyle \begin{bmatrix} 54 & 129.60 & 97.20 & 75.6 \end{bmatrix}Evaluate the scalar multiplication
Reflect and check

Recall:

An 8\% increase = 100\% + 8\% = 108 \% = 1.08. This scalar matrix indicates that 100\% of the original amount is included plus 8\% on top of the original amount.

An 8\% decrease = 100\% - 8 \% = 92\% = 0.92. This scalar matrix indicates that resulting matrix is 92\% or the original.

Idea summary

A scalar is a quantity described by a single numerical value. Scalar multiplication is the process of multiplying a matrix by a scalar (number).

Scalar multiplication is used to change each element in the matrix by the same factor.

In general, the multiplication of a matrix by a scalar will appear similar to this: \lambda \begin{bmatrix} a&b\\ c&d \end{bmatrix}= \begin{bmatrix} \lambda a & \lambda b\\ \lambda c & \lambda d\\ \end{bmatrix}

where Lambda, \lambda, represents the scalar quantity.

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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