设x/2＝y/3＝z/4＝t,则x＝2t,y＝3t,z＝4t.∴(xy+2yz+3zx)/(x^2+y^2+z^2)＝(6t^2+24t^2+24t^2)/(4t^2+9t^2+16t^2)＝(54t^2)/(29t^2)＝54/29。
