$$a ^ { 3 } - 3 a ^ { 2 } b + 3 a b ^ { 2 } - b ^ { 3 } a = 2 b = 4$$
$b=2$
$a=\sqrt[3]{\frac{2\sqrt{345}}{9}+6}+\sqrt[3]{-\frac{2\sqrt{345}}{9}+6}+2$
$a = \frac{9 ^ {\frac{2}{3}} \sqrt[3]{2 {(\sqrt{345} + 27)}} + 9 ^ {\frac{2}{3}} \sqrt[3]{2 {(27 - \sqrt{345})}} + 18}{9} = 5.396096124776237$
$b=2$
