(2002^2-2*2002^2-2000)/(2002^3+2002^2-2003)

分子=2002^2-2*2002+1-1-2000
=(2002-1)^2-2001
=2001^2-2001
=2001(2001-1)
=2001*2000
分母=2002^2(2002+1)-2003
=2002^2*2003-2003
=2003(2002^2-1)
=2003(2002+1)(2002-1)
=2003*2003*2001
结果=2000/2003^2