What are the terms in the expression 5x + 9 – 2y – 3z + 9x – 4y + 2

What does 2y mean here? What kind of arithmetic is happening?

If I told you that -2y and -4y are like terms could you find any other like terms in the above expression?

How do you think we could combine the like terms -2y and -4y?

If we apply the same logic to the whole expression above, what will we have? Is that better than what we had before? Why? Have we really changed it?

Let’s try some with the teacher:

Let’s have a go at the following exercise (exercise 2C from page 24 of the textbook):

Here are the answers to the exercise: