已知x/3=y=z/2≠0,∴x=3y,x²=9y²；z=2y,z²=4y².(2x²-2y²+5z²)/(xy+yz+zx)=(18y²-2y²+20y²)/(3y²+2y²+6y²)=(36y²)/(11y²)=36/11=3又3/1...