2005*2003/2004+1/2004＝[(2004+1)(2004-1)+1]/2004＝(2004²-1+1)/2004=2004²/2004=20045/3*1/13+5/9*3/13+5/18*6/13＝5/3×1/13＋5/3×1/13+5/3×1/13＝5/3×1/13×3＝5/13这样就简便了,刚才真麻烦...