2x-y-z=0 ①3x+2y-12z=0 ②①×2+②得7x-14z=0 x=2z把x=2z代入①得y=3z (2z²+3xy+y²)/(y²+z²)=(2z²+18z²+9z²)/(9z²+z²)=29z²/(10z²)=29/10
