Inverse relationship between addition & subtraction

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Inverse relationship between addition & subtraction

  1. 1. Addition and Subtraction + - Finding the Inverse
  2. 2. Question?What doesinverse mean?
  3. 3. DefinitionInverse means to "undo" OR something similar
  4. 4. For example…You could say that messy is the inverse of a clean (they are opposites and “undo” each other).
  5. 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. 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. 7. Let’s Add + =4 1 5
  8. 8. So… 4+1=5What about 1 + 4? Does that equal 5 too? Let’s see… 1+4=5 YES!
  9. 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. 10. Let’s Subtract - =6 4 2
  11. 11. So... 6–4=2 GREAT!Watch what happens when I switch the “-” and the “=” signs and make the “-” a “+” 6=4+2
  12. 12. = +6 4 2 6=4+2 you can also write it like this…4+2=6 OR 2+4=6
  13. 13. Let’s try that again! (+) 5–3=2 --Switch the signs around-- 5=3+2You could also write it like this… 3+2=5 OR 2+3=5
  14. 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. 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. 16. So…what is the inverse?The inverse is what undoes the first equationAddition can undo subtraction and subtraction can undo addition
  17. 17. Let’s keep practicing!

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