$r=\frac{-2s^{2}-7}{3}$

$s=-\frac{\sqrt{-6r-14}}{2}$
$s=\frac{\sqrt{-6r-14}}{2}$

$s=\frac{\sqrt{-6r-14}}{2}$
$s=-\frac{\sqrt{-6r-14}}{2}\text{, }r\leq -\frac{7}{3}$