本帖最後由 laorenjia 於 12-12-20 15:51 編輯
nadal 發表於 12-12-18 11:41
If you agree to a demo using paper strips, then didn't you just also agree to a method utilizing the ...
You have misunderstood me. I meant literally my question. I am genuinely interested in knowing how to use the number line to remove the brackets, just like when I said your proof was elegant. I agree that the number line "is perhaps the most used tool(s) to demonstrate elementary addition/subtraction problems" but I don't know how to show a - ( b - c ) with the number line. Let us start at b, we move backforward by c to reach the point b - c. Using the number line, we then have to jump to the point - ( b - c ) on the other side of zero. Then we move forward by a. The process is clumsy and unconvincing. My understanding is that we normally use the number line to show x – y by starting at x but not starting at y as in our case. In addition, I have not seen any textbook using this method. That is why I added the note that using paper strips of different length is easier for kids to understand.
To win an argument is never my purpose of writing in this forum.
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