解:原式=(2000+3)*(2000-3) =2000²-3² =4000000-9 =3999991
2003x1997=2003x2000-2003x3=4006000-6009=3999991
(2000+3)*(2000-3)=2000*2000-3*3=4000000-9=399991
解:原式=(200 2)(2000-3)=2000²-3²=3999991