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#### paulmdrdo

##### Active member

- May 13, 2013

- 386

1.show that there is no axiom for set union that correspond to "Existence of additive inverses" for real numbers, by demonstrating that in general it is impossible to find a set X such that $A\cup X=\emptyset$. what is the only set $\emptyset$ which possesses an inverse in this sense?

2. show that the operation of subtraction is not commutative,that is, it is possible to find real numbers a and b such that $b-a\not = a-b$. what can be said about a and b if $b-a=a-b?$

what to do? i don't understand what question 1 is asking.

2. show that the operation of subtraction is not commutative,that is, it is possible to find real numbers a and b such that $b-a\not = a-b$. what can be said about a and b if $b-a=a-b?$

what to do? i don't understand what question 1 is asking.

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