平方差
=(2004+2003)(2004-2003)+……+(2+1)(2-1)
=(2004+2003)×1+……+(2+1)×1
=2004+2003+……+2+1
=(2004+1)+(2003+2)++……+(1003+1002)
=2005×1002
=2009010
平方差
=(2004+2003)(2004-2003)+……+(2+1)(2-1)
=(2004+2003)×1+……+(2+1)×1
=2004+2003+……+2+1
=(2004+1)+(2003+2)++……+(1003+1002)
=2005×1002
=2009010