(1-1/2)(1+1/2)*(1-1/3)(1+1/3)*(1-1/4)(1+1/4)*......*(1-1/2003)(1+1/2003)*(1-1/2004)(1+1/2004)=(1/2)*(3/2)*(2/3)*(4/3)*(3/4)*(5/4)*......*(2002/2003)*(2004/2003)*(2003/2004)*(2005/2004)=(1/2)*(2005/2004)=2005/4008