∵2/x=3/y=4/z∴x/2=y/3=z/4设x/2=y/3=z/4=a则x=2a,y=3a,z=4a把上述结果代入xy-yz+xz=8得2a*3a-3a*4a+2a*4a=8即2a^2=8a^2=4(x+y)(y-z）（x^2-xy+y^2)=(x^3+y^3)(y-z)=［(2a)^3+(3a)^3］(3a-4a)=35a^3*(-a)= -35a^4= -35*4^2= -560
