m-2m-3m+4m-5m-6m= m-2m-3m+4m-5m-6m+・・・+2002m-2003m-2004m

m-2m-3m+4m-5m-6m= m-2m-3m+4m-5m-6m+・・・+2002m-2003m-2004m

m-2m-3m+4m-5m-6m+・・・+2002m-2003m-2004m
=[(1-2-3)+(4-5-6)+・・(2004-2005)]m
=-(4+7+11+・・・+2005)m
=-668*(4+2005)m/2
=-671006m
等差数列式:
Sn=n(a1+an)/2
an=a1+(n-1)d