x²-xy+2y²=14
(x-y)x+2y²=14
6x+2y²=14
6(y+6)+2y²=14
2y²+6y+22=0
y²+3y+11=0
其判别式3²-4*1*11<0,无解
如果原题为x²+xy-2y²=14：
(x-y)(x+2y)=14
则x+2y=14/6=7/3
则x-2y =[4(x-y)-(x+2y)]/3
=65/9