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## Homework Statement

Simply like the title says, "If a is an element of R can you assume -a is an element of R?"

R={All Real Numbers}

## Homework Equations

N/A

## The Attempt at a Solution

I concluded that if a is a real number so must -a. Can that be assumed in a proof? Should a simple "If a [tex]\epsilon[/tex] R, then -a [tex]\epsilon[/tex] R" be sufficient?

EDIT: It has to do with a proof on groups in Abstract Algebra.

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