$$\left. \begin{array} { l } { 2 a ^ { 2 } - a b - 3 b ^ { 2 } + 9 a = 3 b = 2 } \\ { ( x + y ) ^ { 3 } - ( x - y ) ^ { 3 } \text { w h \right.$$
$a=\frac{-\sqrt{25b^{2}+6b+81}+b-9}{4}\text{, }b\in \mathrm{R}$
$a=\frac{\sqrt{25b^{2}+6b+81}+b-9}{4}\text{, }b\in \mathrm{R}$
