Dat :$\left\{ \begin{array}{l} x^2-3x=a\\ y^2+4y=b \end{array} \right.$he tro thanh: $\left\{ \begin{array}{l} a+b=1\\ 3a-2b=3 \end{array} \right.\Leftrightarrow \left\{ \begin{array}{l} a=1\\ b=0 \end{array} \right.$
$\Leftrightarrow \left\{ \begin{array}{l} x^2-3x=1\\ y^2+4y=0 \end{array} \right.$
Ket qua: $(x;y)=(\frac{3-\sqrt{13}}{2};0);(\frac{3-\sqrt{13}}{2};-4);(\frac{3+\sqrt{13}}{2};0);(\frac{3+\sqrt{13}}{2};-4)$