confused with variables in equations
- Thread starter bobisaka
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Dr.Peterson
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If you start with 8, subtract a number m from it, and then add m back to the result, you are back to the original number, 8.
That is, (8 - m + m) = (8 + -m) + m = 8 + (-m + m) = 8 + 0 = 8. There, I first rewrite a subtraction as addition of the opposite; then applied the associative property, then used the fact that any number plus its opposite is zero.
That is, (8 - m + m) = (8 + -m) + m = 8 + (-m + m) = 8 + 0 = 8. There, I first rewrite a subtraction as addition of the opposite; then applied the associative property, then used the fact that any number plus its opposite is zero.
Steven G
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I think it is worth stating what Dr Peterson said again: If you start with 8, subtract a number m from it, and then add m back to the result, you are back to the original number, 8.
You must understand that m is just a place holder for a number. If you are not sure if 8-m+m = 8 or 8-m+m = 8m then replace m with a number. Say m=2
8 - 2 + 2 = 6+2 = 8 which is NOT 8*2=16. Do you see where I got 8*2 from?
Suppose m=5. 8-5+5 = 3+5 = 8 which is not 8*5=40.
Students like to use a calculator but in my opinion they do not know how to use one.
Suppose you are doing a long calculation on your calculator and your calculator show 8. Then you subtract some number (call it m) by mistake and you forgot the number was 8 before you did this subtraction. How do you undue subtracting this number m? Answer is that you add m back.
You must understand that m is just a place holder for a number. If you are not sure if 8-m+m = 8 or 8-m+m = 8m then replace m with a number. Say m=2
8 - 2 + 2 = 6+2 = 8 which is NOT 8*2=16. Do you see where I got 8*2 from?
Suppose m=5. 8-5+5 = 3+5 = 8 which is not 8*5=40.
Students like to use a calculator but in my opinion they do not know how to use one.
Suppose you are doing a long calculation on your calculator and your calculator show 8. Then you subtract some number (call it m) by mistake and you forgot the number was 8 before you did this subtraction. How do you undue subtracting this number m? Answer is that you add m back.