Question

G es to prove that if a, b, and c are integers, where a ≠ 0 and c ≠ 0, such that ac | bc, then a |

Answer 1

$ac\mid bc$ means there exists an integer $n$ such that $ac=bcn$. We can divide both sides by $c$ because $c\neq0$. This implies $a=bn$ for some integer, which is identically $a\mid b$.