1. ## Divisibilty proofs?

Mathematical signs

2. Originally Posted by thegarden
Proofs required for the following divisibility rules:

1. a|1 implies a= plus or minus 1
2. a|b and b|a IF AND ONLY IF (IFF) a= plus or minus b
3. a|b IFF -a|b IFF a|(-b) IFF (-a)(-b)
4. Let b>0. If a|b implies a is less than or equal to b
Sorry for not inserting mathematical signs, new to the forum so just finding my way around, many thanks.
Use definition of division. I do the first one. $a|1 \implies 1 = ab \implies a=\pm 1$.

And second one $a|b \implies a = bc$, $b|a\implies b = ad$.
Thus, $a = bc = adb \implies 1 = bd \implies d = \pm 1$ (assuming $a\not = 0$).