tu pt tren ta co$(2x-y)(7x-4y-12)=0$
$=>y=2x$ the vao pt sau ta co
$\sqrt{15x^2+12x+36}+\sqrt{x^2+8x+32}=6$ vo nghiem vi
can dau tien lon hon 2;can sau lon hon hoac bang 4=>vo nghiem
hoac $y=\frac{7x-12}4$ the vao pt sau
$\sqrt{14x^2+36}+\sqrt{x^2+8x+32}=6$ vo nghiem vt>vp