Question Number 69247 by Rio Michael last updated on 21/Sep/19
$${show}\:{that}\: \\ $$$$\:{c}\mid{a}\:\Leftrightarrow\:−{c}\mid{a}. \\ $$
Commented by kaivan.ahmadi last updated on 22/Sep/19
$${c}\mid{a}\Rightarrow{a}={cx};\:\exists{x}\in\mathbb{Z} \\ $$$$\Rightarrow{a}=−{c}\left(−{x}\right) \\ $$$$\Rightarrow−{c}\mid{a} \\ $$