2004^3-2*2004^2-2002 = 2004^2 (2004-1) - 2004*(2004-1) - 2*(2004 - 1)
= (2004+1) * (2004-2) * (2004-1)
2004^3-2004^2-2003 = 2004^2 (2004-1) - (2004-1)
= (2004 +1 ) * (2004-1) * (2004-1)
原式 = [(2004+1) * (2004-2) * (2004-1)] / [ (2004 +1 ) * (2004-1) * (2004-1) ]
= 2002 / 2003