①x^2-2xy=0
x=2y
②x平方-y平方+2y-1=0
4y^2-y^2+2y-1=0
3y^2+2y-1=0
3 1
1 -1
(3y+1)(y-1)=0
y=-1/3 x=-2/3
y=1 x=2
①x-y-3=0 ②x平方+y+1=0
x=y+3
(y+3)^2+y+1=0
y^2+6y+9+y+1=0
y^2+7y+10=0
(y+5)(y+2)=0
y=-5 x=-2
y=-2 x=1