xy/x+y=2,xz/x+z=3,yz/y+z=4,求7x+5?

xy/x+y=2,xz/x+z=3,yz/y+z=4,求7x+5?: xy/(x+y)=2,(x+y)/xy=1/x+1/y=1/2,1/x+1/z=1/3,1/y+1/z=1/4,x=24/7,y=24/5,z=24,7x+5y-2z=0