Positive Numbers: 1,2,3,4,5,6.... Negative Numbers: -1,-2,-3,-4,-5. Numbers can only be positive or negative unless they are 0. There is no way to magically change a positive number into a negative number and vice versa. A number is either positive, negative or 0. Numbers are fixed as they are constants.
Now...
n+(+n)=n+n
n+(-n)=n-n
n-(-n)=n+n
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(-n)*(-n)=n^2
(-n)*(n)=-n^2
(n)*(n)=n^2
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If n>0,
(n)/(n)=n/n
(-n)/(n)=-(n/n)
(-n)/(-n)=n/n