$$49ax^{2}+kax+1=0$$
$a=-\frac{1}{x\left(49x+k\right)}$
$x\neq -\frac{k}{49}\text{ and }x\neq 0$
$k=\frac{-49ax^{2}-1}{ax}$
$x\neq 0\text{ and }a\neq 0$
