2001/2002×2003
=(1-1/2002)×2003
=1×2003-1/2002×2003
=2003-2003/2002
=2003-1-1/2002
=2001+1-1/2002
=2001又2002分之2001
2001/2002×2003
=2001/2002×(1+2002)
=2001/2002×1+2001/2002×2002
=2001/2002+2001
=2001又2002分之2001