两个非负数加起来等于0,说明他们都是0则a=1,b=2=1/2+1/6...+1/(2004*2005)=1-1/2+1/2-1/3+1/3-1/4....-1/2004+1/2004-1/2005=2004/2005
a=1,b=2原式=1/1-1/2+1/2-1/3+...+1/2004-1/2005 =1-1/2005=2004/2005
