（x/a+y/b+z/c)^2=(x/a)^2+(y/b)^2+(z/c)^2+2(xyc+xzb+yza)/(abc)=1对a/x+b/y+c/z=0通分可知：xyc+xzb+yza所以得证。如果满意，请采纳哦~~
