Drawing Equations on the Number LineDate: 05/09/2002 at 01:21:46 From: Toni Balmer Subject: integers I can't figure out how to draw a certain equation on a number line. 2 + 5 = 7 is easy -2 + 5 = 3 is easy 2 + (-5) = -3 is easy but I get stuck on 2 - (-5) = 7 I know that I will change the signs and add, but how do I show this on a number line? Date: 05/09/2002 at 12:18:45 From: Doctor Peterson Subject: Re: integers Hi, Toni. You have to decide how to represent subtraction. One way is to say that, whereas you add by putting two "arrows" head to tail: o----------> 5 o---------------> + 7 o---------------------------> 12 you subtract by following the second arrow backwards, putting them head to head and reading the answer from the tail of the first to the tail of the second: o---------------------------> 12 o---------------> - 7 o----------> 5 Now if you subtract a negative number, it looks like this: o----------> 5 <---------------o - -7 o---------------------------> 12 Do you see how this is the same as changing the subtraction of -7 to addition of +7? - Doctor Peterson, The Math Forum http://mathforum.org/dr.math/ |
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