Minus versus Plus Negative

							Algebra Skills 1 Class Notes

Minus versus Plus Negative
We have just learned the subtraction rule of “change, change”. It is an EXCELLENT rule, but, we are going to move on. We know that…

4 – 10 = 4 + -10 = -6
Change, change! In the example above, it is often easier to think of 4 – 10 as 4 + -10. But sometimes it is not. Let’s look at the next example.

We know that…

10 – 4 = 10 + -4 = 6

Change, change!

In the example above, IS IT EASIER TO THINK 10 – 4 OR 10 + -4?

If you have 10 – 4 and 10 + -4, both problems give you the same answer. If you were to check other examples using different numbers, you would find the same thing happens. So in algebra, sometime we use….

10 – 4

10 + -4 Adding a negative

Subtracting

They are the same thing!

How do we use this information?
1. We don’t have to always do “change, change”. Example> You don’t have use it for 10 – 8. 2. When we have expressions that need to be simplified by combining like terms, we can make the process a little easier and write our answers more simply. Example> 4x – 7 – 2x –10

4x – 7 – 2x –10 4x – 2x -7 + -10

This is easy to do without change change. (4 – 2)

When you look at the problem, you know the 7 is negative and the 10 is negative.

You answer could be… 2x + -17 but, in an algebra book it will be written as… 2x – 17. Let’s try a couple. 1. 5x – 10 – 3x – 4 2. 8a – 9 – 6a – 3