Inverse relationship between addition & subtraction

1. Addition and Subtraction + - Finding the Inverse

2. Question? What does inverse mean?

3. Definition Inverse means to "undo" OR something similar

4. For example… You could say that messy is the inverse of a clean (they are opposites and “undo” each other).

5. In math, we say that… Addition is the inverse of subtraction Subtraction is the inverse of addition Because these two operations “undo” each other

6. Let’s Count on to 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

7. Let’s Add 4 1 5 + =

8. So… 4 + 1 = 5 What about 1 + 4? Does that equal 5 too? Let’s see… 1 + 4 = 5 YES!

9. Let’s Count back from 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

10. Let’s Subtract - = 6 4 2

11. So... 6 – 4 = 2 GREAT! Watch what happens when I switch the “-” and the “=” signs and make the “-” a “+” 6 = 4 + 2

12. = + 6 4 2 6 = 4 + 2 you can also write it like this… 4 + 2 = 6 OR 2 + 4 = 6

13. Let’s try that again! 5 – 3 = 2 --Switch the signs around-- 5 = 3 + 2 You could also write it like this… 3 + 2 = 5 OR 2 + 3 = 5 (+)

14. Let’s try that one more time! This time we are going to start with addition 5 + 4 = 9 4 + 5 = 9 --Switch the signs-- (remember, when doing subtraction you ALWAYS start with the bigger number) 9 – 4 = 5 OR 9 – 5 = 4

15. Here are some more examples of the inverse at work… 9 + 1 = 10 10 – 1 = 9 1 + 9 = 10 10 – 9 = 1 2 + 2 = 4 4 – 2 = 2 6 + 4 = 10 10 – 4 = 6 4 + 6 = 10 10 – 6 = 4

16. So…what is the inverse? The inverse is what undoes the first equation Addition can undo subtraction and subtraction can undo addition

17. Let’s keep practicing!