│1/2003-1/2002│+│1/2004-1/2003│-│1/2004-1/2002│
去绝对值,分子相同,分母越大,值越小.
故：原式=(1/2002-1/2003) + (1/2003-1/2004)-(1/2002-1/2004)
=1/2002-1/2003 + 1/2003-1/2004-1/2002 +1/2004
=0