$$R _ { n } = \frac { h ^ { n } } { n ^ { n } } f ^ { n } ( a + 0 )$$
$R_{n}=\frac{af^{n}h^{n}}{n^{n}}$
$\left\{\begin{matrix}a=\frac{R_{n}n^{n}}{f^{n}h^{n}}\text{, }&\left(h\neq 0\text{ and }f\neq 0\right)\text{ or }n=0\\a\in \mathrm{C}\text{, }&\left(f=0\text{ or }h=0\right)\text{ and }R_{n}=0\text{ and }n\neq 0\end{matrix}\right.$
