2+3xz+4zx)≥6(xy+yz+xz)+3(xy+yz+zx)=9(xy+yz+zx)≥9
P2=(2x2+3xy+4y2−−−−−−−−−−−−−√+2y2+3yz+4z2−−−−−−−−−−−−−√+2z2+3xz+4x2−−−−−−−−−−−−−√)2≥(2x2+3xy+4y2−−−−−−−−−−−−−√)2+(2y2+3yz+4z2−−−−−−−−−−−−−√)2+2z2+3xz+4x2−−−−−−−−−−−−−√)2=6(x2+y2+z2)+3(xy+yz+zx)≥6(xy+yz+xz)+3(xy+yz+zx)=9(xy+yz+zx)≥9.(xy−−√+yz−−√+zx−−√)23=9.13=3=>P≥3√
2+3xz+4zx)≥6(xy+yz+xz)+3(xy+yz+zx)=9(xy+yz+zx)≥9