x:y:z=3:1:2,所以x/3=y/1=z/2所以x=3y,z=2y代入zx-xy-yz=996y^2-3y^2-2y^2=99y^2=99所以x^2=(3y)^2=9y^2z^2=(2y)^2=4y^2所以2x^2+12y^2+9z^2=2*9y^2+12y^2+9*4y^2=66y^2=66*99=6534