2004的2次方
=(2000+4)^2
=2000^2+8x2000+16
=4016016
2001乘以1999
=(2000+1)(2000-1)
=2000^2-1
=3999999
99的2次方
=(100-1)^2
=100^2-2x100+1
=9801
2004的2次方
=(2000+4)^2
=2000^2+8x2000+16
=4016016
2001乘以1999
=(2000+1)(2000-1)
=2000^2-1
=3999999
99的2次方
=(100-1)^2
=100^2-2x100+1
=9801