1-3+5-7+9-11+…+2005-2007+2009=_.
问题描述:
1-3+5-7+9-11+…+2005-2007+2009=______.
答
1-3+5-7+9-11+…+2005-2007+2009,
=2009-[(3-1)+(7-5)+(11-9)+…+(2007-2005)],
=2009-2×1004÷2,
=2009-1004,
=1005;
故答案为:1005.