999²-1得多少?

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999²-1得多少?
999²-1得多少?

999²-1得多少?
999²-1
= 999x 1000 - 999 -1
= 999000 -1000
= 998000
2003²
= 2003 x 2000 + 2003 x 3
= 4006000 + 6009
= 4012009

（999+1）*（999-1）=998000
2003²=2003 x 2000 + 2003 x 3=4012009

999²-1
=999²-1²
=(999+1)(999-1)
=1000x998
=998000

2003²
=(2000+3)²
=2000²+2x2000x3+3²
=4000000+12000+9
=4012009