Inverse relationship between addition & subtraction
- 1. Addition and Subtraction + - Finding the Inverse
- 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