2001x2002-2000x2003=(2000+1)*(2000+2)-2000*(2000+3)=(4000000+4000+2000+2)-(4000000+6000)=4000+2000+2-6000=2
=2001x2002-(2000x2002+2000)
=(2001-2000)x2002-2000
=2002-2000
=2
2001x2002-2000x2003
=(2000+1)x(2000+2)-2000x(2000+3)
=2000x2000+2000x2+1x2000+1x2-2000x2000-2000x3
=2000x(2+1)-2000x3+2
=2000x3-2000x3+2
=2
=(1+2000)*2002-2000*2003=2002+2000*2002-2000*2003=2002+2000*(2002-2003)=2002-2000=2