A matrix is a set of numbers arranged into rows and columns, like A below:

A above is a 5×4 matrix. This means that it has 5 rows and 4 columns. The number of rows always comes first.

If matrices are the same size we can add and subtract them. If they aren’t the same size, then we can’t. Let’s try adding and subtracting some matrices.

Exercise

Let’s complete exercise 19H from pages 312 and 313:

The answers are below:

Multiplication

We can multiply a matrix by another matrix or by a scalar (that means just by a number).

Let’s try some examples of both. When we are multiplying a matrix by a matrix we will have lots of little multiplications to do – the important thing is that we do them in the right order. The teacher will demonstrate this on the board with some examples.

Exercise

Let’s complete questions 3 to 5 of exercise 19I and all of the questions in exercise 19K:

The answers are below: