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Opposite numbers. Number modulus

Numbers aa and a-a are opposites if they are the same distance from 00 but on different sides of the origin. The absolute value a|a| is the distance from 00 to aa; it is always non-negative. Useful facts: a=a|-a|=|a|, a=0|a|=0 only when a=0a=0.
Opposites: same distance from 00, opposite signs
a|a| — distance, never negative
a=a|-a|=|a|
Opposite and absolute value
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