$$A=7a(x^{2}+3n(-1))$$
$\left\{\begin{matrix}a=-\frac{A}{7\left(3n-x^{2}\right)}\text{, }&n\neq \frac{x^{2}}{3}\\a\in \mathrm{C}\text{, }&A=0\text{ and }n=\frac{x^{2}}{3}\end{matrix}\right.$
$\left\{\begin{matrix}a=-\frac{A}{7\left(3n-x^{2}\right)}\text{, }&n\neq \frac{x^{2}}{3}\\a\in \mathrm{R}\text{, }&A=0\text{ and }n=\frac{x^{2}}{3}\end{matrix}\right.$
$A=7a\left(x^{2}-3n\right)$
