1.
{2x+y=3x22y+x=3y2
Tru 2 ve cua pt cho nhau ta dk
(x−y)(1+3(x+y)x2.y2)=0
TH1:x=y de dang giai dk x=y=1
TH2:1+3x+3yx2y2=0<=>−3(x+y)=x2y2
Cong hai ve cua hpt ban dau co
3(x+y)=3x2+3y2x2y2<=>3(x+y)=3x2+3y2−3(x+y)
<=>−3(x+y)2=x2+y2<=>2x2+3xy+2y2=0(vonghiem)