$\left\{\begin{matrix}C<0\text{, }&A>0\text{ and }B\neq 0\\C>0\text{, }&A<0\text{ and }B\neq 0\end{matrix}\right.$

$B\neq 0$
$\left(C>0\text{ and }A<0\right)\text{ or }\left(A>0\text{ and }C<0\right)$