4x-3y-6z=0得4x-3y=6z,①x+2y-7z=0,得x+2y=7z②②*4-①得11y=22z,即y=2z代入①得x=3z(5x²+2y²-z²)/(2x²-3y²-10z²)=(45z²+8z²-z²)/(18z²-12z²-10z²)=52z²/-4z²=-13
