Prove $ g | f $ and $ f | g \iff $ when $ f = c \cdot g $

Prove $ g | f $ and $ f | g \iff $ when $ f = c \cdot g $

Let $ f, g \in F[x] $, where $ F $ is a field. Prove that, $ g | f $ and $
f | g \iff $ when $ f = c \cdot g $ for $ c \in F^*$. I don't know nothing
about it, so I please at help.