x:y:z=1:2:3
y=2x,z=3x
xy+yz+zx=2x^2+6x^2+3x^2=11x^2=66
x^2=6
y^2=4x^2=24
z^2=9x^2=54
2x的平方+12y的平方-9z的平方
=2*6+12*24-9*54
=12+288-486
=-186