4x-3y-6z=0 ,x+2y-7z=0
解得 x=3z,y=2z
2x^2+3y^2+6z^2=2*9z^2+3*4z^2+6z^2=36z ^2
x^2+5y^2+7z^2=9z^2+5*4z^2+7z^2=36z^2
（2x^2+3y^2+6z^2）/(x^2+5y^2+7z^2)
=1