999²+1999
=999²+999+1000
=999*(999+1)+1000
=999*1000+1000
=1000*(999+1)
=1000*1000
=1000000
999²+1999
=999²+1998+1
=999²+2*999+1
=(999+1)²
=1000²
=1000000
999²+1999
=999²+999+1000
=999*(999+1)+1000
=999*1000+1000
=1000*(999+1)
=1000*1000
=1000000
999²+1999
=999²+1998+1
=999²+2*999+1
=(999+1)²
=1000²
=1000000