$\left \{ {{x . y = 1200}(1) \atop {-x+5y=-295=>x=5y+295}} \right(*).$
Thay (*) vào (1) → (5y +295)y = 1200
⇔ 5y² +295y - 1200 = 0 \(\left[ \begin{array}{l}y1=3,8\\y2 =-62,8\end{array} \right.\)
Thay y vào (*) \(\left[ \begin{array}{l}x1=314\\x2=-19\end{array} \right.\)