$P=a^{3}+b^{3}\text{, }a=R-b\text{, }b=\frac{\sqrt{R^{2}-4Q}+R}{2}\text{, }Q\leq \frac{R^{2}}{4}\text{, }R\in \mathrm{R}\text{, }c=QR$
$P=a^{3}+b^{3}\text{, }a=R-b\text{, }b=\frac{-\sqrt{R^{2}-4Q}+R}{2}\text{, }Q\leq \frac{R^{2}}{4}\text{, }R\in \mathrm{R}\text{, }c=QR$