一、 x1^2+x2^2+…+x10^2-(y1^2+y2^2+…+y10^2)
=(x1^2-y1^2)+(x2^2-y2^2)+...+(x10^2-y10^2)
=(x1+y1)(x1-y1)+(x2+y2)(x2-y2)+...+(x10+y10)(x10-y10)
=10(x1-y1)+10(x2-y2)+...+10(x10-y10)
=10((x1+x2+...+x10)-(y1+y2+...+y1))
(全部选手的所有胜场之和与所有负场之和相等)
=10*0
=0
所以x1^2+x2^2+…+x10^2=y1^2+y2^2+…+y10^2.
三、2004