1-1/2^2=(2+1)(2-1)/2*21-1/3^2=(3+1)(3-1)/3*3----1-1/2004^2=(2004+1)(2004-1)/2004*20041-1/2005^2=(2005+1)(2005-1)/2005*2005原式=(1*2*3*----2004*2006)/(2*2*3*4*---2005)=2006/2*2005=1003/2005